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	$101.54	10.114%	$111.8098	$111.81	$111.80	$111.80
Purchase #2	$158.93	5.553%	$167.7554	$167.76	$167.75	$167.80
Purchase #3	$70.91	4.250%	$73.9237	$73.92	$73.90	$73.90
Purchase #4	$183.43	9.347%	$200.5752	$200.58	$200.60	$200.60
Purchase #5	$31.81	10.434%	$35.1291	$35.13	$35.15	$35.10
Purchase #6	$183.49	7.643%	$197.5141	$197.51	$197.50	$197.50
Purchase #7	$67.37	4.497%	$70.3996	$70.40	$70.40	$70.40
7 purchase totals =	$797.48		$857.1069	$857.11	$857.10	$857.10