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 $60.29   4.739%   $63.1471   $63.15   $63.15   $63.10  
  Purchase #2 $248.91   13.315%   $282.0524   $282.05   $282.05   $282.10  
  Purchase #3 $204.79   13.236%   $231.896   $231.90   $231.90   $231.90  
  Purchase #4 $36.37   7.136%   $38.9654   $38.97   $38.95   $39.00  
  Purchase #5 $55.97   8.850%   $60.9233   $60.92   $60.90   $60.90  
  Purchase #6 $60.92   8.664%   $66.1981   $66.20   $66.20   $66.20  
  Purchase #7 $215.43   12.169%   $241.6457   $241.65   $241.65   $241.60  
  7 purchase totals = $882.68       $984.8280   $984.84   $984.80   $984.80