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 $237.96   4.765%   $249.2988   $249.30   $249.30   $249.30  
  Purchase #2 $56.71   7.358%   $60.8827   $60.88   $60.90   $60.90  
  Purchase #3 $224.36   9.143%   $244.8732   $244.87   $244.85   $244.90  
  Purchase #4 $187.57   7.627%   $201.876   $201.88   $201.90   $201.90  
  Purchase #5 $171.25   10.326%   $188.9333   $188.93   $188.95   $188.90  
  Purchase #6 $248.65   12.112%   $278.7665   $278.77   $278.75   $278.80  
  Purchase #7 $115.73   6.166%   $122.8659   $122.87   $122.85   $122.90  
  7 purchase totals = $1,242.23       $1,347.4964   $1,347.50   $1,347.50   $1,347.60