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 $98.89   12.203%   $110.9575   $110.96   $110.95   $111.00  
  Purchase #2 $226.57   4.367%   $236.4643   $236.46   $236.45   $236.50  
  Purchase #3 $41.88   12.167%   $46.9755   $46.98   $47.00   $47.00  
  Purchase #4 $153.93   10.117%   $169.5031   $169.50   $169.50   $169.50  
  Purchase #5 $21.44   7.763%   $23.1044   $23.10   $23.10   $23.10  
  Purchase #6 $104.26   11.765%   $116.5262   $116.53   $116.55   $116.50  
  Purchase #7 $221.78   13.305%   $251.2878   $251.29   $251.30   $251.30  
  7 purchase totals = $868.75       $954.8188   $954.82   $954.85   $954.90