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	$17.48	7.748%	$18.8344	$18.83	$18.85	$18.80
Purchase #2	$150.77	5.669%	$159.3172	$159.32	$159.30	$159.30
Purchase #3	$132.29	12.261%	$148.5101	$148.51	$148.50	$148.50
Purchase #4	$211.38	6.472%	$225.0605	$225.06	$225.05	$225.10
Purchase #5	$57.80	3.687%	$59.9311	$59.93	$59.95	$59.90
Purchase #6	$40.52	12.812%	$45.7114	$45.71	$45.70	$45.70
Purchase #7	$242.48	5.500%	$255.8164	$255.82	$255.80	$255.80
7 purchase totals =	$852.72		$913.1811	$913.18	$913.15	$913.10