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	$144.31	3.867%	$149.8905	$149.89	$149.90	$149.90
Purchase #2	$17.76	13.328%	$20.1271	$20.13	$20.15	$20.10
Purchase #3	$106.87	4.647%	$111.8362	$111.84	$111.85	$111.80
Purchase #4	$44.42	4.825%	$46.5633	$46.56	$46.55	$46.60
Purchase #5	$160.37	13.194%	$181.5292	$181.53	$181.55	$181.50
Purchase #6	$6.87	10.270%	$7.5755	$7.58	$7.60	$7.60
Purchase #7	$203.29	10.186%	$223.9971	$224.00	$224.00	$224.00
7 purchase totals =	$683.89		$741.5189	$741.53	$741.60	$741.50