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	$38.31	13.743%	$43.5749	$43.57	$43.55	$43.60
Purchase #2	$84.40	7.757%	$90.9469	$90.95	$90.95	$90.90
Purchase #3	$174.90	6.790%	$186.7757	$186.78	$186.80	$186.80
Purchase #4	$246.43	13.522%	$279.7523	$279.75	$279.75	$279.80
Purchase #5	$14.33	11.288%	$15.9476	$15.95	$15.95	$15.90
Purchase #6	$100.82	8.525%	$109.4149	$109.41	$109.40	$109.40
Purchase #7	$166.44	3.851%	$172.8496	$172.85	$172.85	$172.80
7 purchase totals =	$825.63		$899.2619	$899.26	$899.25	$899.20