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	$186.31	6.389%	$198.2133	$198.21	$198.20	$198.20
Purchase #2	$79.86	4.604%	$83.5368	$83.54	$83.55	$83.50
Purchase #3	$152.61	13.852%	$173.7495	$173.75	$173.75	$173.70
Purchase #4	$161.98	6.523%	$172.546	$172.55	$172.55	$172.50
Purchase #5	$84.94	8.821%	$92.4326	$92.43	$92.45	$92.40
Purchase #6	$57.26	9.858%	$62.9047	$62.90	$62.90	$62.90
Purchase #7	$119.55	3.461%	$123.6876	$123.69	$123.70	$123.70
7 purchase totals =	$842.51		$907.0705	$907.07	$907.10	$906.90