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 $169.98   12.181%   $190.6853   $190.69   $190.70   $190.70  
  Purchase #2 $210.26   12.410%   $236.3533   $236.35   $236.35   $236.40  
  Purchase #3 $88.70   12.653%   $99.9232   $99.92   $99.90   $99.90  
  Purchase #4 $85.46   9.853%   $93.8804   $93.88   $93.90   $93.90  
  Purchase #5 $113.56   5.549%   $119.8614   $119.86   $119.85   $119.90  
  Purchase #6 $132.74   9.540%   $145.4034   $145.40   $145.40   $145.40  
  Purchase #7 $86.79   5.179%   $91.2849   $91.28   $91.30   $91.30  
  7 purchase totals = $887.49       $977.3919   $977.38   $977.40   $977.50