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 $227.99   4.545%   $238.3521   $238.35   $238.35   $238.40  
  Purchase #2 $98.69   13.462%   $111.9756   $111.98   $112.00   $112.00  
  Purchase #3 $109.71   6.805%   $117.1758   $117.18   $117.20   $117.20  
  Purchase #4 $169.45   5.549%   $178.8528   $178.85   $178.85   $178.90  
  Purchase #5 $197.92   6.312%   $210.4127   $210.41   $210.40   $210.40  
  Purchase #6 $180.48   11.646%   $201.4987   $201.50   $201.50   $201.50  
  Purchase #7 $67.93   12.476%   $76.4049   $76.40   $76.40   $76.40  
  7 purchase totals = $1,052.17       $1,134.6726   $1,134.67   $1,134.70   $1,134.80