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	$99.43	3.188%	$102.5998	$102.60	$102.60	$102.60
Purchase #2	$37.88	10.599%	$41.8949	$41.89	$41.90	$41.90
Purchase #3	$89.89	12.481%	$101.1092	$101.11	$101.10	$101.10
Purchase #4	$15.48	10.635%	$17.1263	$17.13	$17.15	$17.10
Purchase #5	$207.42	7.750%	$223.4951	$223.50	$223.50	$223.50
Purchase #6	$219.61	4.844%	$230.2479	$230.25	$230.25	$230.20
Purchase #7	$232.83	11.206%	$258.9209	$258.92	$258.90	$258.90
7 purchase totals =	$902.54		$975.3941	$975.40	$975.40	$975.30