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 $59.26   3.859%   $61.5468   $61.55   $61.55   $61.50  
  Purchase #2 $203.25   8.436%   $220.3962   $220.40   $220.40   $220.40  
  Purchase #3 $150.94   7.792%   $162.7012   $162.70   $162.70   $162.70  
  Purchase #4 $27.99   6.318%   $29.7584   $29.76   $29.75   $29.80  
  Purchase #5 $132.81   7.470%   $142.7309   $142.73   $142.75   $142.70  
  Purchase #6 $72.73   11.660%   $81.2103   $81.21   $81.20   $81.20  
  Purchase #7 $244.59   7.352%   $262.5723   $262.57   $262.55   $262.60  
  7 purchase totals = $891.57       $960.9161   $960.92   $960.90   $960.90