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 $88.29   6.456%   $93.99   $93.99   $94.00   $94.00  
  Purchase #2 $18.48   5.576%   $19.5104   $19.51   $19.50   $19.50  
  Purchase #3 $45.45   6.743%   $48.5147   $48.51   $48.50   $48.50  
  Purchase #4 $26.92   12.230%   $30.2123   $30.21   $30.20   $30.20  
  Purchase #5 $239.82   12.432%   $269.6344   $269.63   $269.65   $269.60  
  Purchase #6 $86.44   6.823%   $92.3378   $92.34   $92.35   $92.30  
  Purchase #7 $57.96   10.576%   $64.0898   $64.09   $64.10   $64.10  
  7 purchase totals = $563.36       $618.2894   $618.28   $618.30   $618.20