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 $96.76   8.403%   $104.8907   $104.89   $104.90   $104.90  
  Purchase #2 $157.68   10.113%   $173.6262   $173.63   $173.65   $173.60  
  Purchase #3 $84.44   11.857%   $94.4521   $94.45   $94.45   $94.50  
  Purchase #4 $240.75   8.531%   $261.2884   $261.29   $261.30   $261.30  
  Purchase #5 $25.46   5.114%   $26.762   $26.76   $26.75   $26.80  
  Purchase #6 $202.39   7.184%   $216.9297   $216.93   $216.95   $216.90  
  Purchase #7 $77.98   7.223%   $83.6125   $83.61   $83.60   $83.60  
  7 purchase totals = $885.46       $961.5616   $961.56   $961.60   $961.60