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	$16.69	11.305%	$18.5768	$18.58	$18.60	$18.60
Purchase #2	$241.38	8.774%	$262.5587	$262.56	$262.55	$262.60
Purchase #3	$35.61	13.571%	$40.4426	$40.44	$40.45	$40.40
Purchase #4	$211.83	11.567%	$236.3324	$236.33	$236.35	$236.30
Purchase #5	$67.57	3.833%	$70.16	$70.16	$70.15	$70.20
Purchase #6	$75.37	4.470%	$78.739	$78.74	$78.75	$78.70
Purchase #7	$89.72	7.114%	$96.1027	$96.10	$96.10	$96.10
7 purchase totals =	$738.17		$802.9122	$802.91	$802.95	$802.90