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	$44.63	10.492%	$49.3126	$49.31	$49.30	$49.30
Purchase #2	$100.30	13.433%	$113.7733	$113.77	$113.75	$113.80
Purchase #3	$107.66	3.864%	$111.82	$111.82	$111.80	$111.80
Purchase #4	$200.27	9.834%	$219.9646	$219.96	$219.95	$220.00
Purchase #5	$219.88	4.423%	$229.6053	$229.61	$229.60	$229.60
Purchase #6	$112.89	10.238%	$124.4477	$124.45	$124.45	$124.40
Purchase #7	$218.46	11.751%	$244.1312	$244.13	$244.15	$244.10
7 purchase totals =	$1,004.09		$1,093.0547	$1,093.05	$1,093.00	$1,093.00