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	$34.54	11.527%	$38.5214	$38.52	$38.50	$38.50
Purchase #2	$46.91	7.480%	$50.4189	$50.42	$50.40	$50.40
Purchase #3	$136.72	10.558%	$151.1549	$151.15	$151.15	$151.20
Purchase #4	$97.63	7.809%	$105.2539	$105.25	$105.25	$105.30
Purchase #5	$17.42	8.512%	$18.9028	$18.90	$18.90	$18.90
Purchase #6	$27.32	11.592%	$30.4869	$30.49	$30.50	$30.50
Purchase #7	$141.66	12.120%	$158.8292	$158.83	$158.85	$158.80
7 purchase totals =	$502.20		$553.5680	$553.56	$553.55	$553.60