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	$213.81	13.699%	$243.0998	$243.10	$243.10	$243.10
Purchase #2	$241.52	10.490%	$266.8554	$266.86	$266.85	$266.90
Purchase #3	$98.71	8.209%	$106.8131	$106.81	$106.80	$106.80
Purchase #4	$227.75	6.403%	$242.3328	$242.33	$242.35	$242.30
Purchase #5	$51.94	13.829%	$59.1228	$59.12	$59.10	$59.10
Purchase #6	$124.89	13.594%	$141.8675	$141.87	$141.85	$141.90
Purchase #7	$133.42	13.525%	$151.4651	$151.47	$151.45	$151.50
7 purchase totals =	$1,092.04		$1,211.5565	$1,211.56	$1,211.50	$1,211.60