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 $61.54   8.221%   $66.5992   $66.60   $66.60   $66.60  
  Purchase #2 $81.43   3.492%   $84.2735   $84.27   $84.25   $84.30  
  Purchase #3 $220.77   7.243%   $236.7604   $236.76   $236.75   $236.80  
  Purchase #4 $96.53   6.790%   $103.0844   $103.08   $103.10   $103.10  
  Purchase #5 $124.33   8.785%   $135.2524   $135.25   $135.25   $135.30  
  Purchase #6 $185.48   13.541%   $210.5958   $210.60   $210.60   $210.60  
  Purchase #7 $92.53   4.466%   $96.6624   $96.66   $96.65   $96.70  
  7 purchase totals = $862.61       $933.2281   $933.22   $933.20   $933.40