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 $204.89   11.599%   $228.6552   $228.66   $228.65   $228.70  
  Purchase #2 $33.75   3.673%   $34.9896   $34.99   $35.00   $35.00  
  Purchase #3 $123.26   7.232%   $132.1742   $132.17   $132.15   $132.20  
  Purchase #4 $88.75   11.820%   $99.2403   $99.24   $99.25   $99.20  
  Purchase #5 $210.90   6.500%   $224.6085   $224.61   $224.60   $224.60  
  Purchase #6 $175.57   13.425%   $199.1403   $199.14   $199.15   $199.10  
  Purchase #7 $36.61   10.574%   $40.4811   $40.48   $40.50   $40.50  
  7 purchase totals = $873.73       $959.2892   $959.29   $959.30   $959.30