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 $187.76   8.476%   $203.6745   $203.67   $203.65   $203.70  
  Purchase #2 $32.71   3.119%   $33.7302   $33.73   $33.75   $33.70  
  Purchase #3 $171.97   5.642%   $181.6725   $181.67   $181.65   $181.70  
  Purchase #4 $126.60   8.383%   $137.2129   $137.21   $137.20   $137.20  
  Purchase #5 $101.66   3.244%   $104.9579   $104.96   $104.95   $105.00  
  Purchase #6 $186.87   4.105%   $194.541   $194.54   $194.55   $194.50  
  Purchase #7 $144.91   8.595%   $157.365   $157.37   $157.35   $157.40  
  7 purchase totals = $952.48       $1,013.1540   $1,013.15   $1,013.10   $1,013.20