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	$172.39	5.313%	$181.5491	$181.55	$181.55	$181.50
Purchase #2	$61.88	5.394%	$65.2178	$65.22	$65.20	$65.20
Purchase #3	$186.82	6.781%	$199.4883	$199.49	$199.50	$199.50
Purchase #4	$241.87	12.224%	$271.4362	$271.44	$271.45	$271.40
Purchase #5	$5.38	9.422%	$5.8869	$5.89	$5.90	$5.90
Purchase #6	$214.77	3.505%	$222.2977	$222.30	$222.30	$222.30
Purchase #7	$19.31	7.846%	$20.8251	$20.83	$20.85	$20.80
7 purchase totals =	$902.42		$966.7011	$966.72	$966.75	$966.60