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	$97.48	5.113%	$102.4642	$102.46	$102.45	$102.50
Purchase #2	$107.48	11.469%	$119.8069	$119.81	$119.80	$119.80
Purchase #3	$72.40	10.694%	$80.1425	$80.14	$80.15	$80.10
Purchase #4	$18.94	13.229%	$21.4456	$21.45	$21.45	$21.40
Purchase #5	$195.91	7.753%	$211.0989	$211.10	$211.10	$211.10
Purchase #6	$134.39	5.302%	$141.5154	$141.52	$141.50	$141.50
Purchase #7	$138.41	5.559%	$146.1042	$146.10	$146.10	$146.10
7 purchase totals =	$765.01		$822.5777	$822.58	$822.55	$822.50