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	$235.54	12.479%	$264.933	$264.93	$264.95	$264.90
Purchase #2	$159.31	12.580%	$179.3512	$179.35	$179.35	$179.40
Purchase #3	$101.88	5.149%	$107.1258	$107.13	$107.15	$107.10
Purchase #4	$211.42	6.191%	$224.509	$224.51	$224.50	$224.50
Purchase #5	$222.41	3.863%	$231.0017	$231.00	$231.00	$231.00
Purchase #6	$10.37	9.861%	$11.3926	$11.39	$11.40	$11.40
Purchase #7	$29.58	9.719%	$32.4549	$32.45	$32.45	$32.50
7 purchase totals =	$970.51		$1,050.7682	$1,050.76	$1,050.80	$1,050.80