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 $200.43   5.583%   $211.62   $211.62   $211.60   $211.60  
  Purchase #2 $60.82   4.505%   $63.5599   $63.56   $63.55   $63.60  
  Purchase #3 $108.97   4.381%   $113.744   $113.74   $113.75   $113.70  
  Purchase #4 $60.46   9.106%   $65.9655   $65.97   $65.95   $66.00  
  Purchase #5 $99.55   8.243%   $107.7559   $107.76   $107.75   $107.80  
  Purchase #6 $93.35   11.610%   $104.1879   $104.19   $104.20   $104.20  
  Purchase #7 $239.49   12.834%   $270.2261   $270.23   $270.25   $270.20  
  7 purchase totals = $863.07       $937.0593   $937.07   $937.05   $937.10