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 $58.82   6.574%   $62.6868   $62.69   $62.70   $62.70  
  Purchase #2 $78.71   3.315%   $81.3192   $81.32   $81.30   $81.30  
  Purchase #3 $211.30   11.465%   $235.5255   $235.53   $235.55   $235.50  
  Purchase #4 $89.87   9.447%   $98.36   $98.36   $98.35   $98.40  
  Purchase #5 $19.57   5.459%   $20.6383   $20.64   $20.65   $20.60  
  Purchase #6 $185.39   5.472%   $195.5345   $195.53   $195.55   $195.50  
  Purchase #7 $137.60   13.265%   $155.8526   $155.85   $155.85   $155.90  
  7 purchase totals = $781.26       $849.9169   $849.92   $849.95   $849.90