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 $60.26   7.232%   $64.618   $64.62   $64.60   $64.60  
  Purchase #2 $168.27   12.115%   $188.6559   $188.66   $188.65   $188.70  
  Purchase #3 $249.25   4.450%   $260.3416   $260.34   $260.35   $260.30  
  Purchase #4 $136.63   11.622%   $152.5091   $152.51   $152.50   $152.50  
  Purchase #5 $117.28   9.688%   $128.6421   $128.64   $128.65   $128.60  
  Purchase #6 $56.71   7.144%   $60.7614   $60.76   $60.75   $60.80  
  Purchase #7 $93.34   5.739%   $98.6968   $98.70   $98.70   $98.70  
  7 purchase totals = $881.74       $954.2249   $954.23   $954.20   $954.20