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	$20.72	8.557%	$22.493	$22.49	$22.50	$22.50
Purchase #2	$165.44	4.208%	$172.4017	$172.40	$172.40	$172.40
Purchase #3	$42.84	8.420%	$46.4471	$46.45	$46.45	$46.40
Purchase #4	$81.61	11.576%	$91.0572	$91.06	$91.05	$91.10
Purchase #5	$135.39	7.500%	$145.5443	$145.54	$145.55	$145.50
Purchase #6	$72.28	13.603%	$82.1122	$82.11	$82.10	$82.10
Purchase #7	$206.84	9.319%	$226.1154	$226.12	$226.10	$226.10
7 purchase totals =	$725.12		$786.1709	$786.17	$786.15	$786.10