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 $57.66   9.139%   $62.9295   $62.93   $62.95   $62.90  
  Purchase #2 $46.34   10.517%   $51.2136   $51.21   $51.20   $51.20  
  Purchase #3 $10.98   5.319%   $11.564   $11.56   $11.55   $11.60  
  Purchase #4 $246.42   7.129%   $263.9873   $263.99   $264.00   $264.00  
  Purchase #5 $13.84   6.605%   $14.7541   $14.75   $14.75   $14.80  
  Purchase #6 $204.80   5.380%   $215.8182   $215.82   $215.80   $215.80  
  Purchase #7 $122.99   4.637%   $128.693   $128.69   $128.70   $128.70  
  7 purchase totals = $703.03       $748.9597   $748.95   $748.95   $749.00