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	$135.93	13.618%	$154.4409	$154.44	$154.45	$154.40
Purchase #2	$37.27	10.731%	$41.2694	$41.27	$41.25	$41.30
Purchase #3	$123.71	6.466%	$131.7091	$131.71	$131.70	$131.70
Purchase #4	$69.42	13.213%	$78.5925	$78.59	$78.60	$78.60
Purchase #5	$147.87	7.479%	$158.9292	$158.93	$158.95	$158.90
Purchase #6	$89.91	11.271%	$100.0438	$100.04	$100.05	$100.00
Purchase #7	$236.82	8.169%	$256.1658	$256.17	$256.15	$256.20
7 purchase totals =	$840.93		$921.1507	$921.15	$921.15	$921.10