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	$178.40	4.611%	$186.626	$186.63	$186.65	$186.60
Purchase #2	$147.42	9.612%	$161.59	$161.59	$161.60	$161.60
Purchase #3	$70.57	10.583%	$78.0384	$78.04	$78.05	$78.00
Purchase #4	$51.37	8.436%	$55.7036	$55.70	$55.70	$55.70
Purchase #5	$106.79	11.222%	$118.774	$118.77	$118.75	$118.80
Purchase #6	$89.29	11.683%	$99.7218	$99.72	$99.70	$99.70
Purchase #7	$33.36	13.350%	$37.8136	$37.81	$37.80	$37.80
7 purchase totals =	$677.20		$738.2674	$738.26	$738.25	$738.20