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 $107.63   11.259%   $119.7481   $119.75   $119.75   $119.70  
  Purchase #2 $97.81   6.580%   $104.2459   $104.25   $104.25   $104.20  
  Purchase #3 $141.90   8.795%   $154.3801   $154.38   $154.40   $154.40  
  Purchase #4 $146.42   11.121%   $162.7034   $162.70   $162.70   $162.70  
  Purchase #5 $40.98   7.267%   $43.958   $43.96   $43.95   $44.00  
  Purchase #6 $64.28   4.606%   $67.2407   $67.24   $67.25   $67.20  
  Purchase #7 $189.31   6.263%   $201.1665   $201.17   $201.15   $201.20  
  7 purchase totals = $788.33       $853.4427   $853.45   $853.45   $853.40