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	$149.80	6.784%	$159.9624	$159.96	$159.95	$160.00
Purchase #2	$52.73	12.517%	$59.3302	$59.33	$59.35	$59.30
Purchase #3	$55.91	10.505%	$61.7833	$61.78	$61.80	$61.80
Purchase #4	$242.53	8.256%	$262.5533	$262.55	$262.55	$262.60
Purchase #5	$107.60	3.281%	$111.1304	$111.13	$111.15	$111.10
Purchase #6	$71.25	10.540%	$78.7598	$78.76	$78.75	$78.80
Purchase #7	$219.79	10.262%	$242.3448	$242.34	$242.35	$242.30
7 purchase totals =	$899.61		$975.8642	$975.85	$975.90	$975.90