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	$29.54	12.785%	$33.3167	$33.32	$33.30	$33.30
Purchase #2	$118.72	13.287%	$134.4943	$134.49	$134.50	$134.50
Purchase #3	$176.45	7.138%	$189.045	$189.05	$189.05	$189.00
Purchase #4	$59.68	3.576%	$61.8142	$61.81	$61.80	$61.80
Purchase #5	$57.33	4.130%	$59.6977	$59.70	$59.70	$59.70
Purchase #6	$119.68	12.576%	$134.731	$134.73	$134.75	$134.70
Purchase #7	$51.33	8.362%	$55.6222	$55.62	$55.60	$55.60
7 purchase totals =	$612.73		$668.7211	$668.72	$668.70	$668.60