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 $150.82   8.528%   $163.6819   $163.68   $163.70   $163.70  
  Purchase #2 $28.50   4.409%   $29.7566   $29.76   $29.75   $29.80  
  Purchase #3 $16.69   9.846%   $18.3333   $18.33   $18.35   $18.30  
  Purchase #4 $161.89   10.826%   $179.4162   $179.42   $179.40   $179.40  
  Purchase #5 $242.97   5.710%   $256.8436   $256.84   $256.85   $256.80  
  Purchase #6 $248.53   8.145%   $268.7728   $268.77   $268.75   $268.80  
  Purchase #7 $32.67   7.242%   $35.036   $35.04   $35.05   $35.00  
  7 purchase totals = $882.07       $951.8404   $951.84   $951.85   $951.80