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	$157.79	4.390%	$164.717	$164.72	$164.70	$164.70
Purchase #2	$169.28	6.282%	$179.9142	$179.91	$179.90	$179.90
Purchase #3	$111.96	10.113%	$123.2825	$123.28	$123.30	$123.30
Purchase #4	$120.63	3.211%	$124.5034	$124.50	$124.50	$124.50
Purchase #5	$153.25	9.412%	$167.6739	$167.67	$167.65	$167.70
Purchase #6	$78.45	11.114%	$87.1689	$87.17	$87.15	$87.20
Purchase #7	$50.45	10.134%	$55.5626	$55.56	$55.55	$55.60
7 purchase totals =	$841.81		$902.8225	$902.81	$902.75	$902.90