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	$75.66	8.620%	$82.1819	$82.18	$82.20	$82.20
Purchase #2	$43.94	12.396%	$49.3868	$49.39	$49.40	$49.40
Purchase #3	$20.91	5.731%	$22.1084	$22.11	$22.10	$22.10
Purchase #4	$15.73	4.773%	$16.4808	$16.48	$16.50	$16.50
Purchase #5	$43.28	12.160%	$48.5428	$48.54	$48.55	$48.50
Purchase #6	$117.93	4.744%	$123.5246	$123.52	$123.50	$123.50
Purchase #7	$140.78	13.149%	$159.2912	$159.29	$159.30	$159.30
7 purchase totals =	$458.23		$501.5165	$501.51	$501.55	$501.50