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	$99.85	6.667%	$106.507	$106.51	$106.50	$106.50
Purchase #2	$158.65	13.537%	$180.1265	$180.13	$180.15	$180.10
Purchase #3	$132.64	10.360%	$146.3815	$146.38	$146.40	$146.40
Purchase #4	$212.85	13.822%	$242.2701	$242.27	$242.25	$242.30
Purchase #5	$151.67	4.428%	$158.3859	$158.39	$158.40	$158.40
Purchase #6	$124.67	9.780%	$136.8627	$136.86	$136.85	$136.90
Purchase #7	$109.79	10.767%	$121.6111	$121.61	$121.60	$121.60
7 purchase totals =	$990.12		$1,092.1448	$1,092.15	$1,092.15	$1,092.20