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 $186.98   9.767%   $205.2423   $205.24   $205.25   $205.20  
  Purchase #2 $172.75   7.215%   $185.2139   $185.21   $185.20   $185.20  
  Purchase #3 $47.45   9.518%   $51.9663   $51.97   $51.95   $52.00  
  Purchase #4 $199.82   10.579%   $220.959   $220.96   $220.95   $221.00  
  Purchase #5 $53.25   3.539%   $55.1345   $55.13   $55.15   $55.10  
  Purchase #6 $113.52   4.312%   $118.415   $118.42   $118.40   $118.40  
  Purchase #7 $142.80   13.687%   $162.345   $162.35   $162.35   $162.30  
  7 purchase totals = $916.57       $999.2760   $999.28   $999.25   $999.20