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 $247.81   7.360%   $266.0488   $266.05   $266.05   $266.00  
  Purchase #2 $233.93   4.367%   $244.1457   $244.15   $244.15   $244.10  
  Purchase #3 $216.53   8.389%   $234.6947   $234.69   $234.70   $234.70  
  Purchase #4 $84.63   12.411%   $95.1334   $95.13   $95.15   $95.10  
  Purchase #5 $11.72   7.687%   $12.6209   $12.62   $12.60   $12.60  
  Purchase #6 $23.90   5.737%   $25.2711   $25.27   $25.25   $25.30  
  Purchase #7 $60.46   10.680%   $66.9171   $66.92   $66.90   $66.90  
  7 purchase totals = $878.98       $944.8317   $944.83   $944.80   $944.70