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	$79.30	13.272%	$89.8247	$89.82	$89.80	$89.80
Purchase #2	$220.51	3.172%	$227.5046	$227.50	$227.50	$227.50
Purchase #3	$146.56	8.451%	$158.9458	$158.95	$158.95	$158.90
Purchase #4	$53.25	6.467%	$56.6937	$56.69	$56.70	$56.70
Purchase #5	$184.70	8.364%	$200.1483	$200.15	$200.15	$200.10
Purchase #6	$105.62	6.146%	$112.1114	$112.11	$112.10	$112.10
Purchase #7	$20.55	4.454%	$21.4653	$21.47	$21.45	$21.50
7 purchase totals =	$810.49		$866.6938	$866.69	$866.65	$866.60