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	$152.61	4.315%	$159.1951	$159.20	$159.20	$159.20
Purchase #2	$89.26	12.157%	$100.1113	$100.11	$100.10	$100.10
Purchase #3	$81.94	12.824%	$92.448	$92.45	$92.45	$92.40
Purchase #4	$83.90	7.708%	$90.367	$90.37	$90.35	$90.40
Purchase #5	$93.33	13.307%	$105.7494	$105.75	$105.75	$105.70
Purchase #6	$149.78	6.735%	$159.8677	$159.87	$159.85	$159.90
Purchase #7	$34.42	8.109%	$37.2111	$37.21	$37.20	$37.20
7 purchase totals =	$685.24		$744.9496	$744.96	$744.90	$744.90