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 $51.67   11.622%   $57.6751   $57.68   $57.70   $57.70  
  Purchase #2 $90.84   9.370%   $99.3517   $99.35   $99.35   $99.40  
  Purchase #3 $247.33   7.262%   $265.2911   $265.29   $265.30   $265.30  
  Purchase #4 $88.77   5.823%   $93.9391   $93.94   $93.95   $93.90  
  Purchase #5 $242.95   9.269%   $265.469   $265.47   $265.45   $265.50  
  Purchase #6 $43.81   10.547%   $48.4306   $48.43   $48.45   $48.40  
  Purchase #7 $115.75   12.494%   $130.2118   $130.21   $130.20   $130.20  
  7 purchase totals = $881.12       $960.3684   $960.37   $960.40   $960.40