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 $39.53   10.431%   $43.6534   $43.65   $43.65   $43.70  
  Purchase #2 $124.74   4.273%   $130.0701   $130.07   $130.05   $130.10  
  Purchase #3 $178.54   9.459%   $195.4281   $195.43   $195.45   $195.40  
  Purchase #4 $240.38   9.304%   $262.745   $262.75   $262.75   $262.70  
  Purchase #5 $86.84   8.774%   $94.4593   $94.46   $94.45   $94.50  
  Purchase #6 $139.55   11.244%   $155.241   $155.24   $155.25   $155.20  
  Purchase #7 $104.59   7.748%   $112.6936   $112.69   $112.70   $112.70  
  7 purchase totals = $914.17       $994.2905   $994.29   $994.30   $994.30