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 $250.81   10.163%   $276.2998   $276.30   $276.30   $276.30  
  Purchase #2 $68.79   4.546%   $71.9172   $71.92   $71.90   $71.90  
  Purchase #3 $122.64   9.191%   $133.9118   $133.91   $133.90   $133.90  
  Purchase #4 $52.68   12.575%   $59.3045   $59.30   $59.30   $59.30  
  Purchase #5 $35.67   10.175%   $39.2994   $39.30   $39.30   $39.30  
  Purchase #6 $32.51   4.377%   $33.933   $33.93   $33.95   $33.90  
  Purchase #7 $132.77   12.358%   $149.1777   $149.18   $149.20   $149.20  
  7 purchase totals = $695.87       $763.8434   $763.84   $763.85   $763.80