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 $106.69   9.621%   $116.9546   $116.95   $116.95   $117.00  
  Purchase #2 $53.62   13.612%   $60.9188   $60.92   $60.90   $60.90  
  Purchase #3 $162.63   9.726%   $178.4474   $178.45   $178.45   $178.40  
  Purchase #4 $185.29   6.671%   $197.6507   $197.65   $197.65   $197.70  
  Purchase #5 $27.51   10.141%   $30.2998   $30.30   $30.30   $30.30  
  Purchase #6 $107.72   13.716%   $122.4949   $122.49   $122.50   $122.50  
  Purchase #7 $46.98   3.270%   $48.5162   $48.52   $48.50   $48.50  
  7 purchase totals = $690.44       $755.2824   $755.28   $755.25   $755.30