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	$159.64	5.488%	$168.401	$168.40	$168.40	$168.40
Purchase #2	$50.51	10.539%	$55.8332	$55.83	$55.85	$55.80
Purchase #3	$60.70	11.130%	$67.4559	$67.46	$67.45	$67.50
Purchase #4	$149.87	12.865%	$169.1508	$169.15	$169.15	$169.20
Purchase #5	$19.32	3.430%	$19.9827	$19.98	$20.00	$20.00
Purchase #6	$197.50	12.857%	$222.8926	$222.89	$222.90	$222.90
Purchase #7	$174.57	4.195%	$181.8932	$181.89	$181.90	$181.90
7 purchase totals =	$812.11		$885.6094	$885.60	$885.65	$885.70