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 $22.85   11.569%   $25.4935   $25.49   $25.50   $25.50  
  Purchase #2 $205.53   8.677%   $223.3638   $223.36   $223.35   $223.40  
  Purchase #3 $59.83   7.674%   $64.4214   $64.42   $64.40   $64.40  
  Purchase #4 $60.62   11.219%   $67.421   $67.42   $67.40   $67.40  
  Purchase #5 $127.96   5.217%   $134.6357   $134.64   $134.65   $134.60  
  Purchase #6 $125.39   3.708%   $130.0395   $130.04   $130.05   $130.00  
  Purchase #7 $32.91   11.534%   $36.7058   $36.71   $36.70   $36.70  
  7 purchase totals = $635.09       $682.0807   $682.08   $682.05   $682.00