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	$32.29	3.490%	$33.4169	$33.42	$33.40	$33.40
Purchase #2	$48.97	10.419%	$54.0722	$54.07	$54.05	$54.10
Purchase #3	$139.98	13.507%	$158.8871	$158.89	$158.90	$158.90
Purchase #4	$75.27	7.283%	$80.7519	$80.75	$80.75	$80.80
Purchase #5	$111.54	5.190%	$117.3289	$117.33	$117.35	$117.30
Purchase #6	$20.61	9.702%	$22.6096	$22.61	$22.60	$22.60
Purchase #7	$36.74	12.116%	$41.1914	$41.19	$41.20	$41.20
7 purchase totals =	$465.40		$508.2580	$508.26	$508.25	$508.30