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 $236.59   13.216%   $267.8577   $267.86   $267.85   $267.90  
  Purchase #2 $200.61   3.549%   $207.7296   $207.73   $207.75   $207.70  
  Purchase #3 $92.83   3.287%   $95.8813   $95.88   $95.90   $95.90  
  Purchase #4 $146.80   8.483%   $159.253   $159.25   $159.25   $159.30  
  Purchase #5 $200.62   8.427%   $217.5262   $217.53   $217.55   $217.50  
  Purchase #6 $232.89   3.645%   $241.3788   $241.38   $241.40   $241.40  
  Purchase #7 $120.36   4.514%   $125.7931   $125.79   $125.80   $125.80  
  7 purchase totals = $1,230.70       $1,315.4197   $1,315.42   $1,315.50   $1,315.50