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 $201.66   5.583%   $212.9187   $212.92   $212.90   $212.90  
  Purchase #2 $99.97   3.133%   $103.1021   $103.10   $103.10   $103.10  
  Purchase #3 $96.55   13.164%   $109.2598   $109.26   $109.25   $109.30  
  Purchase #4 $59.76   4.166%   $62.2496   $62.25   $62.25   $62.20  
  Purchase #5 $58.77   12.725%   $66.2485   $66.25   $66.25   $66.20  
  Purchase #6 $66.54   4.151%   $69.3021   $69.30   $69.30   $69.30  
  Purchase #7 $12.40   6.133%   $13.1605   $13.16   $13.15   $13.20  
  7 purchase totals = $595.65       $636.2413   $636.24   $636.20   $636.20