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	$52.31	3.611%	$54.1989	$54.20	$54.20	$54.20
Purchase #2	$83.42	7.158%	$89.3912	$89.39	$89.40	$89.40
Purchase #3	$129.54	12.336%	$145.5201	$145.52	$145.50	$145.50
Purchase #4	$62.50	4.327%	$65.2044	$65.20	$65.20	$65.20
Purchase #5	$36.29	11.313%	$40.3955	$40.40	$40.40	$40.40
Purchase #6	$193.48	5.326%	$203.7847	$203.78	$203.80	$203.80
Purchase #7	$188.57	8.548%	$204.689	$204.69	$204.70	$204.70
7 purchase totals =	$746.11		$803.1838	$803.18	$803.20	$803.20