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 $92.71   4.145%   $96.5528   $96.55   $96.55   $96.60  
  Purchase #2 $170.71   13.428%   $193.6329   $193.63   $193.65   $193.60  
  Purchase #3 $11.94   4.252%   $12.4477   $12.45   $12.45   $12.40  
  Purchase #4 $250.99   13.497%   $284.8661   $284.87   $284.85   $284.90  
  Purchase #5 $134.96   8.583%   $146.5436   $146.54   $146.55   $146.50  
  Purchase #6 $51.45   13.236%   $58.2599   $58.26   $58.25   $58.30  
  Purchase #7 $190.48   10.488%   $210.4575   $210.46   $210.45   $210.50  
  7 purchase totals = $903.24       $1,002.7605   $1,002.76   $1,002.75   $1,002.80