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	$212.87	4.524%	$222.5002	$222.50	$222.50	$222.50
Purchase #2	$142.36	12.289%	$159.8546	$159.85	$159.85	$159.90
Purchase #3	$111.62	6.444%	$118.8128	$118.81	$118.80	$118.80
Purchase #4	$42.95	11.181%	$47.7522	$47.75	$47.75	$47.80
Purchase #5	$99.62	5.106%	$104.7066	$104.71	$104.70	$104.70
Purchase #6	$147.69	12.814%	$166.615	$166.62	$166.60	$166.60
Purchase #7	$235.35	8.448%	$255.2324	$255.23	$255.25	$255.20
7 purchase totals =	$992.46		$1,075.4738	$1,075.47	$1,075.45	$1,075.50