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 $95.79   3.183%   $98.839   $98.84   $98.85   $98.80  
  Purchase #2 $115.57   8.657%   $125.5749   $125.57   $125.55   $125.60  
  Purchase #3 $13.68   4.869%   $14.3461   $14.35   $14.35   $14.30  
  Purchase #4 $217.38   5.473%   $229.2772   $229.28   $229.30   $229.30  
  Purchase #5 $98.41   8.513%   $106.7876   $106.79   $106.80   $106.80  
  Purchase #6 $53.67   5.388%   $56.5617   $56.56   $56.55   $56.60  
  Purchase #7 $186.64   11.368%   $207.8572   $207.86   $207.85   $207.90  
  7 purchase totals = $781.14       $839.2437   $839.25   $839.25   $839.30