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 $60.86   6.702%   $64.9388   $64.94   $64.95   $64.90  
  Purchase #2 $248.41   12.813%   $280.2388   $280.24   $280.25   $280.20  
  Purchase #3 $114.82   9.698%   $125.9552   $125.96   $125.95   $126.00  
  Purchase #4 $146.78   6.810%   $156.7757   $156.78   $156.80   $156.80  
  Purchase #5 $15.91   11.128%   $17.6805   $17.68   $17.70   $17.70  
  Purchase #6 $47.63   10.495%   $52.6288   $52.63   $52.65   $52.60  
  Purchase #7 $175.26   5.273%   $184.5015   $184.50   $184.50   $184.50  
  7 purchase totals = $809.67       $882.7193   $882.73   $882.80   $882.70