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	$58.41	12.498%	$65.7101	$65.71	$65.70	$65.70
Purchase #2	$241.86	8.836%	$263.2307	$263.23	$263.25	$263.20
Purchase #3	$114.67	13.444%	$130.0862	$130.09	$130.10	$130.10
Purchase #4	$175.46	13.583%	$199.2927	$199.29	$199.30	$199.30
Purchase #5	$244.94	13.684%	$278.4576	$278.46	$278.45	$278.50
Purchase #6	$91.48	8.569%	$99.3189	$99.32	$99.30	$99.30
Purchase #7	$71.35	10.493%	$78.8368	$78.84	$78.85	$78.80
7 purchase totals =	$998.17		$1,114.9330	$1,114.94	$1,114.95	$1,114.90