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 $206.47   13.318%   $233.9677   $233.97   $233.95   $234.00  
  Purchase #2 $60.36   3.122%   $62.2444   $62.24   $62.25   $62.20  
  Purchase #3 $178.36   8.274%   $193.1175   $193.12   $193.10   $193.10  
  Purchase #4 $35.31   9.698%   $38.7344   $38.73   $38.75   $38.70  
  Purchase #5 $97.69   12.444%   $109.8465   $109.85   $109.85   $109.80  
  Purchase #6 $163.63   7.141%   $175.3148   $175.31   $175.30   $175.30  
  Purchase #7 $31.52   4.460%   $32.9258   $32.93   $32.95   $32.90  
  7 purchase totals = $773.34       $846.1511   $846.15   $846.15   $846.00