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	$202.96	13.345%	$230.045	$230.05	$230.05	$230.00
Purchase #2	$40.79	4.696%	$42.7055	$42.71	$42.70	$42.70
Purchase #3	$110.81	11.401%	$123.4434	$123.44	$123.45	$123.40
Purchase #4	$63.37	10.857%	$70.2501	$70.25	$70.25	$70.30
Purchase #5	$47.58	11.720%	$53.1564	$53.16	$53.15	$53.20
Purchase #6	$104.85	6.399%	$111.5594	$111.56	$111.55	$111.60
Purchase #7	$38.46	10.133%	$42.3572	$42.36	$42.35	$42.40
7 purchase totals =	$608.82		$673.5170	$673.53	$673.50	$673.60