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 $60.53   4.823%   $63.4494   $63.45   $63.45   $63.40  
  Purchase #2 $107.49   8.507%   $116.6342   $116.63   $116.65   $116.60  
  Purchase #3 $241.38   6.796%   $257.7842   $257.78   $257.80   $257.80  
  Purchase #4 $113.78   11.869%   $127.2845   $127.28   $127.30   $127.30  
  Purchase #5 $115.74   5.181%   $121.7365   $121.74   $121.75   $121.70  
  Purchase #6 $111.90   6.749%   $119.4521   $119.45   $119.45   $119.50  
  Purchase #7 $121.95   11.162%   $135.5621   $135.56   $135.55   $135.60  
  7 purchase totals = $872.77       $941.9030   $941.89   $941.95   $941.90