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 $32.55   3.241%   $33.6049   $33.60   $33.60   $33.60  
  Purchase #2 $103.35   13.147%   $116.9374   $116.94   $116.95   $116.90  
  Purchase #3 $21.93   8.346%   $23.7603   $23.76   $23.75   $23.80  
  Purchase #4 $184.80   4.237%   $192.63   $192.63   $192.65   $192.60  
  Purchase #5 $86.29   5.796%   $91.2914   $91.29   $91.30   $91.30  
  Purchase #6 $68.48   3.662%   $70.9877   $70.99   $71.00   $71.00  
  Purchase #7 $35.72   13.367%   $40.4947   $40.49   $40.50   $40.50  
  7 purchase totals = $533.12       $569.7064   $569.70   $569.75   $569.70