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 $200.93   11.654%   $224.3464   $224.35   $224.35   $224.30  
  Purchase #2 $65.59   5.722%   $69.3431   $69.34   $69.35   $69.30  
  Purchase #3 $222.78   8.606%   $241.9524   $241.95   $241.95   $242.00  
  Purchase #4 $173.32   13.703%   $197.07   $197.07   $197.05   $197.10  
  Purchase #5 $207.46   13.249%   $234.9464   $234.95   $234.95   $234.90  
  Purchase #6 $244.44   11.201%   $271.8197   $271.82   $271.80   $271.80  
  Purchase #7 $250.90   9.445%   $274.5975   $274.60   $274.60   $274.60  
  7 purchase totals = $1,365.42       $1,514.0755   $1,514.08   $1,514.05   $1,514.00