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 $86.98   10.566%   $96.1703   $96.17   $96.15   $96.20  
  Purchase #2 $210.92   12.634%   $237.5676   $237.57   $237.55   $237.60  
  Purchase #3 $11.34   13.700%   $12.8936   $12.89   $12.90   $12.90  
  Purchase #4 $199.63   13.671%   $226.9214   $226.92   $226.90   $226.90  
  Purchase #5 $59.30   11.864%   $66.3354   $66.34   $66.35   $66.30  
  Purchase #6 $28.45   13.847%   $32.3895   $32.39   $32.40   $32.40  
  Purchase #7 $108.68   11.429%   $121.101   $121.10   $121.10   $121.10  
  7 purchase totals = $705.30       $793.3788   $793.38   $793.35   $793.40