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 $33.31   5.199%   $35.0418   $35.04   $35.05   $35.00  
  Purchase #2 $22.66   6.153%   $24.0543   $24.05   $24.05   $24.10  
  Purchase #3 $198.91   4.276%   $207.4154   $207.42   $207.40   $207.40  
  Purchase #4 $14.91   13.621%   $16.9409   $16.94   $16.95   $16.90  
  Purchase #5 $237.73   6.810%   $253.9194   $253.92   $253.90   $253.90  
  Purchase #6 $64.98   10.736%   $71.9563   $71.96   $71.95   $72.00  
  Purchase #7 $163.40   13.162%   $184.9067   $184.91   $184.90   $184.90  
  7 purchase totals = $735.90       $794.2348   $794.24   $794.20   $794.20