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	$145.80	12.644%	$164.235	$164.24	$164.25	$164.20
Purchase #2	$100.67	13.379%	$114.1386	$114.14	$114.15	$114.10
Purchase #3	$50.57	10.284%	$55.7706	$55.77	$55.75	$55.80
Purchase #4	$37.92	10.216%	$41.7939	$41.79	$41.80	$41.80
Purchase #5	$126.89	13.520%	$144.0455	$144.05	$144.05	$144.00
Purchase #6	$224.45	6.389%	$238.7901	$238.79	$238.80	$238.80
Purchase #7	$119.41	10.251%	$131.6507	$131.65	$131.65	$131.70
7 purchase totals =	$805.71		$890.4244	$890.43	$890.45	$890.40