Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $218.27   10.693%   $241.6096   $241.61   $241.60   $241.60  
  Purchase #2 $174.63   13.644%   $198.4565   $198.46   $198.45   $198.50  
  Purchase #3 $244.36   12.459%   $274.8048   $274.80   $274.80   $274.80  
  Purchase #4 $129.35   11.621%   $144.3818   $144.38   $144.40   $144.40  
  Purchase #5 $194.76   6.181%   $206.7981   $206.80   $206.80   $206.80  
  Purchase #6 $115.88   8.707%   $125.9697   $125.97   $125.95   $126.00  
  Purchase #7 $234.59   12.507%   $263.9302   $263.93   $263.95   $263.90  
  7 purchase totals = $1,311.84       $1,455.9507   $1,455.95   $1,455.95   $1,456.00