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 $239.75   9.123%   $261.6224   $261.62   $261.60   $261.60  
  Purchase #2 $221.31   10.599%   $244.7666   $244.77   $244.75   $244.80  
  Purchase #3 $24.61   10.756%   $27.2571   $27.26   $27.25   $27.30  
  Purchase #4 $74.53   6.113%   $79.086   $79.09   $79.10   $79.10  
  Purchase #5 $89.36   9.575%   $97.9162   $97.92   $97.90   $97.90  
  Purchase #6 $105.25   12.560%   $118.4694   $118.47   $118.45   $118.50  
  Purchase #7 $187.46   3.841%   $194.6603   $194.66   $194.65   $194.70  
  7 purchase totals = $942.27       $1,023.7780   $1,023.79   $1,023.70   $1,023.90