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 $62.83   10.728%   $69.5704   $69.57   $69.55   $69.60  
  Purchase #2 $153.65   4.682%   $160.8439   $160.84   $160.85   $160.80  
  Purchase #3 $201.55   4.152%   $209.9184   $209.92   $209.90   $209.90  
  Purchase #4 $25.57   9.375%   $27.9672   $27.97   $27.95   $28.00  
  Purchase #5 $106.63   13.792%   $121.3364   $121.34   $121.35   $121.30  
  Purchase #6 $215.82   3.855%   $224.1399   $224.14   $224.15   $224.10  
  Purchase #7 $202.30   12.507%   $227.6017   $227.60   $227.60   $227.60  
  7 purchase totals = $968.35       $1,041.3779   $1,041.38   $1,041.35   $1,041.30