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 $30.92   9.447%   $33.841   $33.84   $33.85   $33.80  
  Purchase #2 $245.65   13.822%   $279.6037   $279.60   $279.60   $279.60  
  Purchase #3 $227.30   7.433%   $244.1952   $244.20   $244.20   $244.20  
  Purchase #4 $245.77   6.867%   $262.647   $262.65   $262.65   $262.60  
  Purchase #5 $117.84   6.211%   $125.159   $125.16   $125.15   $125.20  
  Purchase #6 $244.73   9.383%   $267.693   $267.69   $267.70   $267.70  
  Purchase #7 $102.48   10.485%   $113.225   $113.23   $113.25   $113.20  
  7 purchase totals = $1,214.69       $1,326.3639   $1,326.37   $1,326.40   $1,326.30