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	$81.67	9.181%	$89.1681	$89.17	$89.15	$89.20
Purchase #2	$174.89	11.660%	$195.2822	$195.28	$195.30	$195.30
Purchase #3	$233.52	7.697%	$251.494	$251.49	$251.50	$251.50
Purchase #4	$86.86	8.719%	$94.4333	$94.43	$94.45	$94.40
Purchase #5	$83.31	13.454%	$94.5185	$94.52	$94.50	$94.50
Purchase #6	$15.35	3.493%	$15.8862	$15.89	$15.90	$15.90
Purchase #7	$147.87	11.869%	$165.4207	$165.42	$165.40	$165.40
7 purchase totals =	$823.47		$906.2030	$906.20	$906.20	$906.20