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 $200.37   9.229%   $218.8621   $218.86   $218.85   $218.90  
  Purchase #2 $136.82   9.711%   $150.1066   $150.11   $150.10   $150.10  
  Purchase #3 $28.50   13.528%   $32.3555   $32.36   $32.35   $32.40  
  Purchase #4 $183.76   11.106%   $204.1684   $204.17   $204.15   $204.20  
  Purchase #5 $93.43   6.808%   $99.7907   $99.79   $99.80   $99.80  
  Purchase #6 $54.44   8.251%   $58.9318   $58.93   $58.95   $58.90  
  Purchase #7 $110.37   4.337%   $115.1567   $115.16   $115.15   $115.20  
  7 purchase totals = $807.69       $879.3718   $879.38   $879.35   $879.50