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	$145.89	13.191%	$165.1343	$165.13	$165.15	$165.10
Purchase #2	$183.27	12.685%	$206.5178	$206.52	$206.50	$206.50
Purchase #3	$218.26	13.130%	$246.9175	$246.92	$246.90	$246.90
Purchase #4	$238.47	11.868%	$266.7716	$266.77	$266.75	$266.80
Purchase #5	$79.94	3.321%	$82.5948	$82.59	$82.60	$82.60
Purchase #6	$125.89	9.167%	$137.4303	$137.43	$137.45	$137.40
Purchase #7	$190.71	11.249%	$212.163	$212.16	$212.15	$212.20
7 purchase totals =	$1,182.43		$1,317.5293	$1,317.52	$1,317.50	$1,317.50