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 $186.53   12.153%   $209.199   $209.20   $209.20   $209.20  
  Purchase #2 $90.51   3.173%   $93.3819   $93.38   $93.40   $93.40  
  Purchase #3 $9.28   5.209%   $9.7634   $9.76   $9.75   $9.80  
  Purchase #4 $66.91   3.864%   $69.4954   $69.50   $69.50   $69.50  
  Purchase #5 $214.54   13.251%   $242.9687   $242.97   $242.95   $243.00  
  Purchase #6 $32.95   5.486%   $34.7576   $34.76   $34.75   $34.80  
  Purchase #7 $244.76   9.368%   $267.6891   $267.69   $267.70   $267.70  
  7 purchase totals = $845.48       $927.2551   $927.26   $927.25   $927.40