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 $67.86   10.182%   $74.7695   $74.77   $74.75   $74.80  
  Purchase #2 $182.35   6.800%   $194.7498   $194.75   $194.75   $194.70  
  Purchase #3 $178.86   9.451%   $195.7641   $195.76   $195.75   $195.80  
  Purchase #4 $18.34   11.150%   $20.3849   $20.38   $20.40   $20.40  
  Purchase #5 $98.65   8.865%   $107.3953   $107.40   $107.40   $107.40  
  Purchase #6 $57.55   7.717%   $61.9911   $61.99   $62.00   $62.00  
  Purchase #7 $160.80   5.859%   $170.2213   $170.22   $170.20   $170.20  
  7 purchase totals = $764.41       $825.2760   $825.27   $825.25   $825.30