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 $20.31   11.247%   $22.5943   $22.59   $22.60   $22.60  
  Purchase #2 $115.73   8.208%   $125.2291   $125.23   $125.25   $125.20  
  Purchase #3 $19.69   7.796%   $21.225   $21.23   $21.25   $21.20  
  Purchase #4 $114.96   9.152%   $125.4811   $125.48   $125.50   $125.50  
  Purchase #5 $88.28   11.148%   $98.1215   $98.12   $98.10   $98.10  
  Purchase #6 $206.30   13.683%   $234.528   $234.53   $234.55   $234.50  
  Purchase #7 $233.84   12.153%   $262.2586   $262.26   $262.25   $262.30  
  7 purchase totals = $799.11       $889.4376   $889.44   $889.50   $889.40