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 $237.79   11.559%   $265.2761   $265.28   $265.30   $265.30  
  Purchase #2 $229.88   8.689%   $249.8543   $249.85   $249.85   $249.90  
  Purchase #3 $15.36   7.756%   $16.5513   $16.55   $16.55   $16.60  
  Purchase #4 $175.63   8.581%   $190.7008   $190.70   $190.70   $190.70  
  Purchase #5 $76.27   5.133%   $80.1849   $80.18   $80.20   $80.20  
  Purchase #6 $98.41   11.782%   $110.0047   $110.00   $110.00   $110.00  
  Purchase #7 $44.79   13.347%   $50.7681   $50.77   $50.75   $50.80  
  7 purchase totals = $878.13       $963.3402   $963.33   $963.35   $963.50