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 $59.37   9.572%   $65.0529   $65.05   $65.05   $65.10  
  Purchase #2 $76.94   5.692%   $81.3194   $81.32   $81.30   $81.30  
  Purchase #3 $158.59   5.778%   $167.7533   $167.75   $167.75   $167.80  
  Purchase #4 $46.56   4.626%   $48.7139   $48.71   $48.70   $48.70  
  Purchase #5 $14.47   9.828%   $15.8921   $15.89   $15.90   $15.90  
  Purchase #6 $100.56   4.161%   $104.7443   $104.74   $104.75   $104.70  
  Purchase #7 $223.34   12.763%   $251.8449   $251.84   $251.85   $251.80  
  7 purchase totals = $679.83       $735.3208   $735.30   $735.30   $735.30