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 $234.53   13.141%   $265.3496   $265.35   $265.35   $265.30  
  Purchase #2 $99.41   12.626%   $111.9615   $111.96   $111.95   $112.00  
  Purchase #3 $226.91   6.379%   $241.3846   $241.38   $241.40   $241.40  
  Purchase #4 $206.81   4.396%   $215.9014   $215.90   $215.90   $215.90  
  Purchase #5 $115.71   5.623%   $122.2164   $122.22   $122.20   $122.20  
  Purchase #6 $76.27   10.374%   $84.1822   $84.18   $84.20   $84.20  
  Purchase #7 $77.89   5.752%   $82.3702   $82.37   $82.35   $82.40  
  7 purchase totals = $1,037.53       $1,123.3659   $1,123.36   $1,123.35   $1,123.40