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 $232.26   5.851%   $245.8495   $245.85   $245.85   $245.80  
  Purchase #2 $76.57   6.328%   $81.4153   $81.42   $81.40   $81.40  
  Purchase #3 $203.94   3.688%   $211.4613   $211.46   $211.45   $211.50  
  Purchase #4 $22.97   13.371%   $26.0413   $26.04   $26.05   $26.00  
  Purchase #5 $176.78   8.545%   $191.8859   $191.89   $191.90   $191.90  
  Purchase #6 $111.58   5.511%   $117.7292   $117.73   $117.75   $117.70  
  Purchase #7 $60.32   7.419%   $64.7951   $64.80   $64.80   $64.80  
  7 purchase totals = $884.42       $939.1776   $939.19   $939.20   $939.10