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 $97.88   6.444%   $104.1874   $104.19   $104.20   $104.20  
  Purchase #2 $32.87   11.210%   $36.5547   $36.55   $36.55   $36.60  
  Purchase #3 $243.78   11.496%   $271.8049   $271.80   $271.80   $271.80  
  Purchase #4 $196.67   10.609%   $217.5347   $217.53   $217.55   $217.50  
  Purchase #5 $167.88   9.527%   $183.8739   $183.87   $183.85   $183.90  
  Purchase #6 $118.63   6.607%   $126.4679   $126.47   $126.45   $126.50  
  Purchase #7 $237.32   10.357%   $261.8992   $261.90   $261.90   $261.90  
  7 purchase totals = $1,095.03       $1,202.3227   $1,202.31   $1,202.30   $1,202.40