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 $58.36   11.560%   $65.1064   $65.11   $65.10   $65.10  
  Purchase #2 $241.69   12.230%   $271.2487   $271.25   $271.25   $271.20  
  Purchase #3 $184.33   11.779%   $206.0422   $206.04   $206.05   $206.00  
  Purchase #4 $114.61   9.351%   $125.3272   $125.33   $125.35   $125.30  
  Purchase #5 $13.96   3.663%   $14.4714   $14.47   $14.45   $14.50  
  Purchase #6 $97.44   4.174%   $101.5071   $101.51   $101.50   $101.50  
  Purchase #7 $234.99   10.551%   $259.7838   $259.78   $259.80   $259.80  
  7 purchase totals = $945.38       $1,043.4868   $1,043.49   $1,043.50   $1,043.40