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 $239.92   8.772%   $260.9658   $260.97   $260.95   $261.00  
  Purchase #2 $189.66   12.267%   $212.9256   $212.93   $212.95   $212.90  
  Purchase #3 $89.45   8.491%   $97.0452   $97.05   $97.05   $97.00  
  Purchase #4 $132.57   13.483%   $150.4444   $150.44   $150.45   $150.40  
  Purchase #5 $206.27   5.325%   $217.2539   $217.25   $217.25   $217.30  
  Purchase #6 $132.41   5.582%   $139.8011   $139.80   $139.80   $139.80  
  Purchase #7 $226.37   5.347%   $238.474   $238.47   $238.45   $238.50  
  7 purchase totals = $1,216.65       $1,316.9100   $1,316.91   $1,316.90   $1,316.90