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 $244.53   9.624%   $268.0636   $268.06   $268.05   $268.10  
  Purchase #2 $189.56   9.135%   $206.8763   $206.88   $206.90   $206.90  
  Purchase #3 $83.63   4.616%   $87.4904   $87.49   $87.50   $87.50  
  Purchase #4 $119.40   13.508%   $135.5286   $135.53   $135.55   $135.50  
  Purchase #5 $151.63   7.250%   $162.6232   $162.62   $162.60   $162.60  
  Purchase #6 $49.46   4.196%   $51.5353   $51.54   $51.55   $51.50  
  Purchase #7 $51.82   7.187%   $55.5443   $55.54   $55.55   $55.50  
  7 purchase totals = $890.03       $967.6617   $967.66   $967.70   $967.60