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	$159.60	8.371%	$172.9601	$172.96	$172.95	$173.00
Purchase #2	$151.84	13.766%	$172.7423	$172.74	$172.75	$172.70
Purchase #3	$158.88	12.782%	$179.188	$179.19	$179.20	$179.20
Purchase #4	$184.46	13.460%	$209.2883	$209.29	$209.30	$209.30
Purchase #5	$33.60	4.371%	$35.0687	$35.07	$35.05	$35.10
Purchase #6	$169.37	6.459%	$180.3096	$180.31	$180.30	$180.30
Purchase #7	$65.83	7.412%	$70.7093	$70.71	$70.70	$70.70
7 purchase totals =	$923.58		$1,020.2663	$1,020.27	$1,020.25	$1,020.30