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	$249.69	10.340%	$275.5079	$275.51	$275.50	$275.50
Purchase #2	$192.50	13.807%	$219.0785	$219.08	$219.10	$219.10
Purchase #3	$202.89	3.105%	$209.1897	$209.19	$209.20	$209.20
Purchase #4	$59.33	10.191%	$65.3763	$65.38	$65.40	$65.40
Purchase #5	$250.29	11.527%	$279.1409	$279.14	$279.15	$279.10
Purchase #6	$158.86	5.644%	$167.8261	$167.83	$167.85	$167.80
Purchase #7	$29.70	12.603%	$33.4431	$33.44	$33.45	$33.40
7 purchase totals =	$1,143.26		$1,249.5625	$1,249.57	$1,249.65	$1,249.50