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	$164.52	13.448%	$186.6446	$186.64	$186.65	$186.60
Purchase #2	$186.87	11.560%	$208.4722	$208.47	$208.45	$208.50
Purchase #3	$165.60	8.147%	$179.0914	$179.09	$179.10	$179.10
Purchase #4	$77.96	3.211%	$80.4633	$80.46	$80.45	$80.50
Purchase #5	$72.81	7.485%	$78.2598	$78.26	$78.25	$78.30
Purchase #6	$224.91	4.742%	$235.5752	$235.58	$235.60	$235.60
Purchase #7	$157.54	9.259%	$172.1266	$172.13	$172.15	$172.10
7 purchase totals =	$1,050.21		$1,140.6331	$1,140.63	$1,140.65	$1,140.70