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 $100.87   4.608%   $105.5181   $105.52   $105.50   $105.50  
  Purchase #2 $178.26   7.630%   $191.8612   $191.86   $191.85   $191.90  
  Purchase #3 $81.75   10.599%   $90.4147   $90.41   $90.40   $90.40  
  Purchase #4 $182.99   12.656%   $206.1492   $206.15   $206.15   $206.10  
  Purchase #5 $132.58   12.204%   $148.7601   $148.76   $148.75   $148.80  
  Purchase #6 $144.25   3.526%   $149.3363   $149.34   $149.35   $149.30  
  Purchase #7 $16.33   11.393%   $18.1905   $18.19   $18.20   $18.20  
  7 purchase totals = $837.03       $910.2301   $910.23   $910.20   $910.20