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	$131.51	6.155%	$139.6044	$139.60	$139.60	$139.60
Purchase #2	$181.59	8.284%	$196.6329	$196.63	$196.65	$196.60
Purchase #3	$29.76	13.371%	$33.7392	$33.74	$33.75	$33.70
Purchase #4	$164.76	7.781%	$177.58	$177.58	$177.60	$177.60
Purchase #5	$68.92	4.707%	$72.1641	$72.16	$72.15	$72.20
Purchase #6	$29.90	9.274%	$32.6729	$32.67	$32.65	$32.70
Purchase #7	$205.47	13.748%	$233.718	$233.72	$233.70	$233.70
7 purchase totals =	$811.91		$886.1115	$886.10	$886.10	$886.10