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	$164.66	4.523%	$172.1076	$172.11	$172.10	$172.10
Purchase #2	$126.33	9.622%	$138.4855	$138.49	$138.50	$138.50
Purchase #3	$16.34	10.590%	$18.0704	$18.07	$18.05	$18.10
Purchase #4	$90.27	13.130%	$102.1225	$102.12	$102.10	$102.10
Purchase #5	$80.74	10.747%	$89.4171	$89.42	$89.40	$89.40
Purchase #6	$68.82	5.212%	$72.4069	$72.41	$72.40	$72.40
Purchase #7	$46.81	10.305%	$51.6338	$51.63	$51.65	$51.60
7 purchase totals =	$593.97		$644.2438	$644.25	$644.20	$644.20