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	$80.58	3.794%	$83.6372	$83.64	$83.65	$83.60
Purchase #2	$53.68	4.444%	$56.0655	$56.07	$56.05	$56.10
Purchase #3	$132.99	7.393%	$142.822	$142.82	$142.80	$142.80
Purchase #4	$49.64	13.422%	$56.3027	$56.30	$56.30	$56.30
Purchase #5	$52.56	13.113%	$59.4522	$59.45	$59.45	$59.50
Purchase #6	$20.53	3.413%	$21.2307	$21.23	$21.25	$21.20
Purchase #7	$56.73	4.373%	$59.2108	$59.21	$59.20	$59.20
7 purchase totals =	$446.71		$478.7211	$478.72	$478.70	$478.70