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 $24.84   4.743%   $26.0182   $26.02   $26.00   $26.00  
  Purchase #2 $125.60   9.861%   $137.9854   $137.99   $138.00   $138.00  
  Purchase #3 $55.28   3.610%   $57.2756   $57.28   $57.30   $57.30  
  Purchase #4 $99.51   7.217%   $106.6916   $106.69   $106.70   $106.70  
  Purchase #5 $249.34   5.660%   $263.4526   $263.45   $263.45   $263.50  
  Purchase #6 $172.25   5.103%   $181.0399   $181.04   $181.05   $181.00  
  Purchase #7 $173.76   13.665%   $197.5043   $197.50   $197.50   $197.50  
  7 purchase totals = $900.58       $969.9676   $969.97   $970.00   $970.00