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 $225.95   3.124%   $233.0087   $233.01   $233.00   $233.00  
  Purchase #2 $68.36   10.145%   $75.2951   $75.30   $75.30   $75.30  
  Purchase #3 $43.38   9.253%   $47.394   $47.39   $47.40   $47.40  
  Purchase #4 $72.57   7.158%   $77.7646   $77.76   $77.75   $77.80  
  Purchase #5 $123.44   9.669%   $135.3754   $135.38   $135.40   $135.40  
  Purchase #6 $215.98   9.303%   $236.0726   $236.07   $236.05   $236.10  
  Purchase #7 $177.74   7.630%   $191.3016   $191.30   $191.30   $191.30  
  7 purchase totals = $927.42       $996.2120   $996.21   $996.20   $996.30