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 $239.53   11.719%   $267.6005   $267.60   $267.60   $267.60  
  Purchase #2 $247.98   3.698%   $257.1503   $257.15   $257.15   $257.20  
  Purchase #3 $233.64   5.667%   $246.8804   $246.88   $246.90   $246.90  
  Purchase #4 $62.26   9.429%   $68.1305   $68.13   $68.15   $68.10  
  Purchase #5 $215.66   8.588%   $234.1809   $234.18   $234.20   $234.20  
  Purchase #6 $6.65   9.346%   $7.2715   $7.27   $7.25   $7.30  
  Purchase #7 $191.97   7.797%   $206.9379   $206.94   $206.95   $206.90  
  7 purchase totals = $1,197.69       $1,288.1520   $1,288.15   $1,288.20   $1,288.20