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 $183.80   12.474%   $206.7272   $206.73   $206.75   $206.70  
  Purchase #2 $115.47   7.394%   $124.0079   $124.01   $124.00   $124.00  
  Purchase #3 $220.40   7.854%   $237.7102   $237.71   $237.70   $237.70  
  Purchase #4 $130.29   12.357%   $146.3899   $146.39   $146.40   $146.40  
  Purchase #5 $64.76   10.294%   $71.4264   $71.43   $71.45   $71.40  
  Purchase #6 $217.85   13.508%   $247.2772   $247.28   $247.30   $247.30  
  Purchase #7 $240.72   7.574%   $258.9521   $258.95   $258.95   $259.00  
  7 purchase totals = $1,173.29       $1,292.4909   $1,292.50   $1,292.55   $1,292.50