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 $236.62   13.261%   $267.9982   $268.00   $268.00   $268.00  
  Purchase #2 $116.99   8.260%   $126.6534   $126.65   $126.65   $126.70  
  Purchase #3 $111.75   9.130%   $121.9528   $121.95   $121.95   $122.00  
  Purchase #4 $6.29   9.120%   $6.8636   $6.86   $6.85   $6.90  
  Purchase #5 $58.32   3.381%   $60.2918   $60.29   $60.30   $60.30  
  Purchase #6 $111.67   6.582%   $119.0201   $119.02   $119.00   $119.00  
  Purchase #7 $55.26   5.817%   $58.4745   $58.47   $58.45   $58.50  
  7 purchase totals = $696.90       $761.2544   $761.24   $761.20   $761.40