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	$20.96	3.659%	$21.7269	$21.73	$21.75	$21.70
Purchase #2	$174.74	3.766%	$181.3207	$181.32	$181.30	$181.30
Purchase #3	$90.77	4.279%	$94.654	$94.65	$94.65	$94.70
Purchase #4	$202.30	12.717%	$228.0265	$228.03	$228.05	$228.00
Purchase #5	$223.60	4.500%	$233.662	$233.66	$233.65	$233.70
Purchase #6	$55.50	7.720%	$59.7846	$59.78	$59.80	$59.80
Purchase #7	$146.52	8.831%	$159.4592	$159.46	$159.45	$159.50
7 purchase totals =	$914.39		$978.6339	$978.63	$978.65	$978.70