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	$67.46	4.404%	$70.4309	$70.43	$70.45	$70.40
Purchase #2	$47.98	11.162%	$53.3355	$53.34	$53.35	$53.30
Purchase #3	$129.59	10.589%	$143.3123	$143.31	$143.30	$143.30
Purchase #4	$227.57	10.496%	$251.4557	$251.46	$251.45	$251.50
Purchase #5	$211.49	12.241%	$237.3785	$237.38	$237.40	$237.40
Purchase #6	$16.64	8.435%	$18.0436	$18.04	$18.05	$18.00
Purchase #7	$142.72	11.695%	$159.4111	$159.41	$159.40	$159.40
7 purchase totals =	$843.45		$933.3676	$933.37	$933.40	$933.30