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	$45.34	10.836%	$50.253	$50.25	$50.25	$50.30
Purchase #2	$144.56	10.764%	$160.1204	$160.12	$160.10	$160.10
Purchase #3	$202.85	10.402%	$223.9505	$223.95	$223.95	$224.00
Purchase #4	$128.57	13.683%	$146.1622	$146.16	$146.15	$146.20
Purchase #5	$114.39	4.584%	$119.6336	$119.63	$119.65	$119.60
Purchase #6	$51.60	5.191%	$54.2786	$54.28	$54.30	$54.30
Purchase #7	$49.67	3.498%	$51.4075	$51.41	$51.40	$51.40
7 purchase totals =	$736.98		$805.8058	$805.80	$805.80	$805.90