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 $239.79   10.826%   $265.7497   $265.75   $265.75   $265.70  
  Purchase #2 $210.42   5.188%   $221.3366   $221.34   $221.35   $221.30  
  Purchase #3 $69.95   11.466%   $77.9705   $77.97   $77.95   $78.00  
  Purchase #4 $41.54   6.655%   $44.3045   $44.30   $44.30   $44.30  
  Purchase #5 $114.73   10.621%   $126.9155   $126.92   $126.90   $126.90  
  Purchase #6 $66.89   10.377%   $73.8312   $73.83   $73.85   $73.80  
  Purchase #7 $116.60   7.440%   $125.275   $125.28   $125.30   $125.30  
  7 purchase totals = $859.92       $935.3830   $935.39   $935.40   $935.30