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	$37.43	3.132%	$38.6023	$38.60	$38.60	$38.60
Purchase #2	$241.41	4.183%	$251.5082	$251.51	$251.50	$251.50
Purchase #3	$108.74	6.729%	$116.0571	$116.06	$116.05	$116.10
Purchase #4	$5.46	4.334%	$5.6966	$5.70	$5.70	$5.70
Purchase #5	$41.30	3.253%	$42.6435	$42.64	$42.65	$42.60
Purchase #6	$127.69	11.307%	$142.1279	$142.13	$142.15	$142.10
Purchase #7	$230.51	3.253%	$238.0085	$238.01	$238.00	$238.00
7 purchase totals =	$792.54		$834.6441	$834.65	$834.65	$834.60