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 $122.67   8.262%   $132.805   $132.81   $132.80   $132.80  
  Purchase #2 $59.38   12.749%   $66.9504   $66.95   $66.95   $67.00  
  Purchase #3 $107.58   8.379%   $116.5941   $116.59   $116.60   $116.60  
  Purchase #4 $105.31   8.293%   $114.0434   $114.04   $114.05   $114.00  
  Purchase #5 $81.29   9.439%   $88.963   $88.96   $88.95   $89.00  
  Purchase #6 $146.94   9.442%   $160.8141   $160.81   $160.80   $160.80  
  Purchase #7 $212.46   11.152%   $236.1535   $236.15   $236.15   $236.20  
  7 purchase totals = $835.63       $916.3235   $916.31   $916.30   $916.40