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	$42.39	7.226%	$45.4531	$45.45	$45.45	$45.50
Purchase #2	$14.26	12.251%	$16.007	$16.01	$16.00	$16.00
Purchase #3	$32.82	12.868%	$37.0433	$37.04	$37.05	$37.00
Purchase #4	$25.81	9.625%	$28.2942	$28.29	$28.30	$28.30
Purchase #5	$48.33	4.403%	$50.458	$50.46	$50.45	$50.50
Purchase #6	$157.53	13.318%	$178.5098	$178.51	$178.50	$178.50
Purchase #7	$211.54	10.222%	$233.1636	$233.16	$233.15	$233.20
7 purchase totals =	$532.68		$588.9290	$588.92	$588.90	$589.00