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 $215.48   12.543%   $242.5077   $242.51   $242.50   $242.50  
  Purchase #2 $86.79   9.225%   $94.7964   $94.80   $94.80   $94.80  
  Purchase #3 $101.26   3.756%   $105.0633   $105.06   $105.05   $105.10  
  Purchase #4 $115.78   6.567%   $123.3833   $123.38   $123.40   $123.40  
  Purchase #5 $98.51   12.492%   $110.8159   $110.82   $110.80   $110.80  
  Purchase #6 $93.90   13.124%   $106.2234   $106.22   $106.20   $106.20  
  Purchase #7 $246.80   5.821%   $261.1662   $261.17   $261.15   $261.20  
  7 purchase totals = $958.52       $1,043.9562   $1,043.96   $1,043.90   $1,044.00