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 $248.87   9.872%   $273.4384   $273.44   $273.45   $273.40  
  Purchase #2 $118.72   3.566%   $122.9536   $122.95   $122.95   $123.00  
  Purchase #3 $194.91   12.526%   $219.3244   $219.32   $219.30   $219.30  
  Purchase #4 $83.34   12.469%   $93.7317   $93.73   $93.75   $93.70  
  Purchase #5 $234.43   11.530%   $261.4598   $261.46   $261.45   $261.50  
  Purchase #6 $246.44   4.240%   $256.8891   $256.89   $256.90   $256.90  
  Purchase #7 $219.88   12.334%   $247   $247.00   $247.00   $247.00  
  7 purchase totals = $1,346.59       $1,474.7970   $1,474.79   $1,474.80   $1,474.80