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	$75.39	12.429%	$84.7602	$84.76	$84.75	$84.80
Purchase #2	$191.91	8.532%	$208.2838	$208.28	$208.30	$208.30
Purchase #3	$79.96	11.867%	$89.4489	$89.45	$89.45	$89.40
Purchase #4	$85.68	3.277%	$88.4877	$88.49	$88.50	$88.50
Purchase #5	$238.35	6.627%	$254.1455	$254.15	$254.15	$254.10
Purchase #6	$144.94	4.382%	$151.2913	$151.29	$151.30	$151.30
Purchase #7	$158.30	9.484%	$173.3132	$173.31	$173.30	$173.30
7 purchase totals =	$974.53		$1,049.7306	$1,049.73	$1,049.75	$1,049.70