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	$30.74	6.242%	$32.6588	$32.66	$32.65	$32.70
Purchase #2	$101.66	9.462%	$111.2791	$111.28	$111.30	$111.30
Purchase #3	$78.40	12.445%	$88.1569	$88.16	$88.15	$88.20
Purchase #4	$78.48	8.481%	$85.1359	$85.14	$85.15	$85.10
Purchase #5	$135.84	12.141%	$152.3323	$152.33	$152.35	$152.30
Purchase #6	$214.55	6.513%	$228.5236	$228.52	$228.50	$228.50
Purchase #7	$61.27	5.513%	$64.6478	$64.65	$64.65	$64.60
7 purchase totals =	$700.94		$762.7344	$762.74	$762.75	$762.70