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 $60.69   5.517%   $64.0383   $64.04   $64.05   $64.00  
  Purchase #2 $198.70   4.496%   $207.6336   $207.63   $207.65   $207.60  
  Purchase #3 $42.68   7.607%   $45.9267   $45.93   $45.95   $45.90  
  Purchase #4 $245.37   4.320%   $255.97   $255.97   $255.95   $256.00  
  Purchase #5 $82.49   12.111%   $92.4804   $92.48   $92.50   $92.50  
  Purchase #6 $71.44   8.195%   $77.2945   $77.29   $77.30   $77.30  
  Purchase #7 $47.60   10.260%   $52.4838   $52.48   $52.50   $52.50  
  7 purchase totals = $748.97       $795.8273   $795.82   $795.90   $795.80