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	$138.81	4.767%	$145.4271	$145.43	$145.45	$145.40
Purchase #2	$82.76	10.322%	$91.3025	$91.30	$91.30	$91.30
Purchase #3	$223.42	4.421%	$233.2974	$233.30	$233.30	$233.30
Purchase #4	$215.96	11.372%	$240.519	$240.52	$240.50	$240.50
Purchase #5	$224.37	13.724%	$255.1625	$255.16	$255.15	$255.20
Purchase #6	$231.58	6.722%	$247.1468	$247.15	$247.15	$247.10
Purchase #7	$26.95	5.770%	$28.505	$28.51	$28.50	$28.50
7 purchase totals =	$1,143.85		$1,241.3603	$1,241.37	$1,241.35	$1,241.30