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 $20.38   7.861%   $21.9821   $21.98   $22.00   $22.00  
  Purchase #2 $238.27   7.785%   $256.8193   $256.82   $256.80   $256.80  
  Purchase #3 $11.77   12.837%   $13.2809   $13.28   $13.30   $13.30  
  Purchase #4 $15.51   5.577%   $16.375   $16.38   $16.40   $16.40  
  Purchase #5 $197.77   3.809%   $205.3031   $205.30   $205.30   $205.30  
  Purchase #6 $106.40   7.361%   $114.2321   $114.23   $114.25   $114.20  
  Purchase #7 $170.54   3.834%   $177.0785   $177.08   $177.10   $177.10  
  7 purchase totals = $760.64       $805.0710   $805.07   $805.15   $805.10