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 $67.60   8.546%   $73.3771   $73.38   $73.40   $73.40  
  Purchase #2 $120.96   11.149%   $134.4458   $134.45   $134.45   $134.40  
  Purchase #3 $173.91   13.475%   $197.3444   $197.34   $197.35   $197.30  
  Purchase #4 $67.64   6.245%   $71.8641   $71.86   $71.85   $71.90  
  Purchase #5 $102.86   11.214%   $114.3947   $114.39   $114.40   $114.40  
  Purchase #6 $35.37   13.756%   $40.2355   $40.24   $40.25   $40.20  
  Purchase #7 $240.84   11.806%   $269.2736   $269.27   $269.25   $269.30  
  7 purchase totals = $809.18       $900.9352   $900.93   $900.95   $900.90