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 $56.83   3.739%   $58.9549   $58.95   $58.95   $59.00  
  Purchase #2 $20.85   3.718%   $21.6252   $21.63   $21.65   $21.60  
  Purchase #3 $116.30   7.594%   $125.1318   $125.13   $125.15   $125.10  
  Purchase #4 $52.77   6.729%   $56.3209   $56.32   $56.30   $56.30  
  Purchase #5 $231.84   13.161%   $262.3525   $262.35   $262.35   $262.40  
  Purchase #6 $175.89   7.624%   $189.2999   $189.30   $189.30   $189.30  
  Purchase #7 $28.64   6.441%   $30.4847   $30.48   $30.50   $30.50  
  7 purchase totals = $683.12       $744.1699   $744.16   $744.20   $744.20