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 $222.44   9.683%   $243.9789   $243.98   $244.00   $244.00  
  Purchase #2 $59.68   10.664%   $66.0443   $66.04   $66.05   $66.00  
  Purchase #3 $227.47   11.679%   $254.0362   $254.04   $254.05   $254.00  
  Purchase #4 $151.28   8.144%   $163.6002   $163.60   $163.60   $163.60  
  Purchase #5 $250.61   5.328%   $263.9625   $263.96   $263.95   $264.00  
  Purchase #6 $112.85   4.164%   $117.5491   $117.55   $117.55   $117.50  
  Purchase #7 $119.73   10.674%   $132.51   $132.51   $132.50   $132.50  
  7 purchase totals = $1,144.06       $1,241.6812   $1,241.68   $1,241.70   $1,241.60