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 $232.35   7.521%   $249.825   $249.83   $249.85   $249.80  
  Purchase #2 $241.66   3.240%   $249.4898   $249.49   $249.50   $249.50  
  Purchase #3 $92.71   9.297%   $101.3292   $101.33   $101.35   $101.30  
  Purchase #4 $68.47   11.778%   $76.5344   $76.53   $76.55   $76.50  
  Purchase #5 $30.70   9.765%   $33.6979   $33.70   $33.70   $33.70  
  Purchase #6 $216.37   7.736%   $233.1084   $233.11   $233.10   $233.10  
  Purchase #7 $68.99   8.657%   $74.9625   $74.96   $74.95   $75.00  
  7 purchase totals = $951.25       $1,018.9472   $1,018.95   $1,019.00   $1,018.90