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 $49.85   5.518%   $52.6007   $52.60   $52.60   $52.60  
  Purchase #2 $237.70   9.157%   $259.4662   $259.47   $259.45   $259.50  
  Purchase #3 $126.98   6.742%   $135.541   $135.54   $135.55   $135.50  
  Purchase #4 $88.95   10.510%   $98.2986   $98.30   $98.30   $98.30  
  Purchase #5 $179.81   13.131%   $203.4209   $203.42   $203.40   $203.40  
  Purchase #6 $177.75   10.188%   $195.8592   $195.86   $195.85   $195.90  
  Purchase #7 $131.82   4.307%   $137.4975   $137.50   $137.50   $137.50  
  7 purchase totals = $992.86       $1,082.6841   $1,082.69   $1,082.65   $1,082.70