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 $224.47   7.753%   $241.8732   $241.87   $241.85   $241.90  
  Purchase #2 $139.77   8.603%   $151.7944   $151.79   $151.80   $151.80  
  Purchase #3 $32.32   8.516%   $35.0724   $35.07   $35.05   $35.10  
  Purchase #4 $34.51   8.351%   $37.3919   $37.39   $37.40   $37.40  
  Purchase #5 $93.68   13.181%   $106.028   $106.03   $106.05   $106.00  
  Purchase #6 $234.71   11.625%   $261.995   $262.00   $262.00   $262.00  
  Purchase #7 $105.71   8.534%   $114.7313   $114.73   $114.75   $114.70  
  7 purchase totals = $865.17       $948.8862   $948.88   $948.90   $948.90