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 $228.69   12.243%   $256.6885   $256.69   $256.70   $256.70  
  Purchase #2 $40.60   10.662%   $44.9288   $44.93   $44.95   $44.90  
  Purchase #3 $127.79   6.714%   $136.3698   $136.37   $136.35   $136.40  
  Purchase #4 $127.92   6.209%   $135.8626   $135.86   $135.85   $135.90  
  Purchase #5 $101.26   7.378%   $108.731   $108.73   $108.75   $108.70  
  Purchase #6 $200.50   7.651%   $215.8403   $215.84   $215.85   $215.80  
  Purchase #7 $59.26   6.832%   $63.3086   $63.31   $63.30   $63.30  
  7 purchase totals = $886.02       $961.7296   $961.73   $961.75   $961.70