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 $227.87   3.118%   $234.975   $234.98   $235.00   $235.00  
  Purchase #2 $128.32   11.189%   $142.6777   $142.68   $142.70   $142.70  
  Purchase #3 $6.92   10.279%   $7.6313   $7.63   $7.65   $7.60  
  Purchase #4 $95.92   3.564%   $99.3386   $99.34   $99.35   $99.30  
  Purchase #5 $63.72   11.265%   $70.8981   $70.90   $70.90   $70.90  
  Purchase #6 $249.51   8.386%   $270.4339   $270.43   $270.45   $270.40  
  Purchase #7 $130.75   11.827%   $146.2138   $146.21   $146.20   $146.20  
  7 purchase totals = $903.01       $972.1684   $972.17   $972.25   $972.10