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 $101.27   3.605%   $104.9208   $104.92   $104.90   $104.90  
  Purchase #2 $238.77   13.358%   $270.6649   $270.66   $270.65   $270.70  
  Purchase #3 $161.71   9.733%   $177.4492   $177.45   $177.45   $177.40  
  Purchase #4 $183.26   6.154%   $194.5378   $194.54   $194.55   $194.50  
  Purchase #5 $58.99   6.111%   $62.5949   $62.59   $62.60   $62.60  
  Purchase #6 $248.73   8.424%   $269.683   $269.68   $269.70   $269.70  
  Purchase #7 $225.28   13.754%   $256.265   $256.27   $256.25   $256.30  
  7 purchase totals = $1,218.01       $1,336.1156   $1,336.11   $1,336.10   $1,336.10