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 $46.59   8.634%   $50.6126   $50.61   $50.60   $50.60  
  Purchase #2 $141.39   3.451%   $146.2694   $146.27   $146.25   $146.30  
  Purchase #3 $197.75   9.450%   $216.4374   $216.44   $216.45   $216.40  
  Purchase #4 $115.78   3.535%   $119.8728   $119.87   $119.85   $119.90  
  Purchase #5 $45.59   13.389%   $51.694   $51.69   $51.70   $51.70  
  Purchase #6 $115.58   5.455%   $121.8849   $121.88   $121.90   $121.90  
  Purchase #7 $132.37   11.485%   $147.5727   $147.57   $147.55   $147.60  
  7 purchase totals = $795.05       $854.3438   $854.33   $854.30   $854.40