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	$131.62	5.707%	$139.1316	$139.13	$139.15	$139.10
Purchase #2	$53.94	6.698%	$57.5529	$57.55	$57.55	$57.60
Purchase #3	$202.33	10.673%	$223.9247	$223.92	$223.90	$223.90
Purchase #4	$65.87	4.534%	$68.8565	$68.86	$68.85	$68.90
Purchase #5	$107.65	3.541%	$111.4619	$111.46	$111.45	$111.50
Purchase #6	$26.39	3.301%	$27.2611	$27.26	$27.25	$27.30
Purchase #7	$229.72	13.382%	$260.4611	$260.46	$260.45	$260.50
7 purchase totals =	$817.52		$888.6498	$888.64	$888.60	$888.80