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	$9.73	7.866%	$10.4954	$10.50	$10.50	$10.50
Purchase #2	$79.81	13.413%	$90.5149	$90.51	$90.50	$90.50
Purchase #3	$77.94	9.761%	$85.5477	$85.55	$85.55	$85.50
Purchase #4	$186.84	3.148%	$192.7217	$192.72	$192.70	$192.70
Purchase #5	$184.61	3.261%	$190.6301	$190.63	$190.65	$190.60
Purchase #6	$102.66	9.804%	$112.7248	$112.72	$112.70	$112.70
Purchase #7	$211.65	8.805%	$230.2858	$230.29	$230.30	$230.30
7 purchase totals =	$853.24		$912.9204	$912.92	$912.90	$912.80