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 $72.84   8.734%   $79.2018   $79.20   $79.20   $79.20  
  Purchase #2 $60.39   11.823%   $67.5299   $67.53   $67.55   $67.50  
  Purchase #3 $91.80   6.342%   $97.622   $97.62   $97.60   $97.60  
  Purchase #4 $202.42   5.568%   $213.6907   $213.69   $213.70   $213.70  
  Purchase #5 $93.72   11.161%   $104.1801   $104.18   $104.20   $104.20  
  Purchase #6 $99.76   11.216%   $110.9491   $110.95   $110.95   $110.90  
  Purchase #7 $59.56   5.240%   $62.6809   $62.68   $62.70   $62.70  
  7 purchase totals = $680.49       $735.8545   $735.85   $735.90   $735.80