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 $173.67   5.484%   $183.1941   $183.19   $183.20   $183.20  
  Purchase #2 $141.97   4.868%   $148.8811   $148.88   $148.90   $148.90  
  Purchase #3 $23.43   3.612%   $24.2763   $24.28   $24.30   $24.30  
  Purchase #4 $208.99   5.723%   $220.9505   $220.95   $220.95   $221.00  
  Purchase #5 $209.32   11.859%   $234.1433   $234.14   $234.15   $234.10  
  Purchase #6 $69.73   11.325%   $77.6269   $77.63   $77.65   $77.60  
  Purchase #7 $230.32   13.873%   $262.2723   $262.27   $262.25   $262.30  
  7 purchase totals = $1,057.43       $1,151.3445   $1,151.34   $1,151.40   $1,151.40