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 $19.70   7.135%   $21.1056   $21.11   $21.10   $21.10  
  Purchase #2 $65.77   6.537%   $70.0694   $70.07   $70.05   $70.10  
  Purchase #3 $63.74   5.869%   $67.4809   $67.48   $67.50   $67.50  
  Purchase #4 $226.63   6.573%   $241.5264   $241.53   $241.55   $241.50  
  Purchase #5 $178.26   10.721%   $197.3713   $197.37   $197.35   $197.40  
  Purchase #6 $100.38   8.867%   $109.2807   $109.28   $109.30   $109.30  
  Purchase #7 $164.47   3.522%   $170.2626   $170.26   $170.25   $170.30  
  7 purchase totals = $818.95       $877.0969   $877.10   $877.10   $877.20