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 $206.99   3.496%   $214.2264   $214.23   $214.25   $214.20  
  Purchase #2 $20.65   3.116%   $21.2935   $21.29   $21.30   $21.30  
  Purchase #3 $146.52   6.732%   $156.3837   $156.38   $156.40   $156.40  
  Purchase #4 $148.93   10.570%   $164.6719   $164.67   $164.65   $164.70  
  Purchase #5 $131.51   3.428%   $136.0182   $136.02   $136.00   $136.00  
  Purchase #6 $205.28   11.256%   $228.3863   $228.39   $228.40   $228.40  
  Purchase #7 $70.25   9.271%   $76.7629   $76.76   $76.75   $76.80  
  7 purchase totals = $930.13       $997.7429   $997.74   $997.75   $997.80