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	$20.61	10.233%	$22.719	$22.72	$22.70	$22.70
Purchase #2	$225.92	3.431%	$233.6713	$233.67	$233.65	$233.70
Purchase #3	$129.55	6.134%	$137.4966	$137.50	$137.50	$137.50
Purchase #4	$172.96	7.189%	$185.3941	$185.39	$185.40	$185.40
Purchase #5	$203.49	10.792%	$225.4506	$225.45	$225.45	$225.50
Purchase #6	$154.53	8.177%	$167.1659	$167.17	$167.15	$167.20
Purchase #7	$71.82	11.408%	$80.0132	$80.01	$80.00	$80.00
7 purchase totals =	$978.88		$1,051.9107	$1,051.91	$1,051.85	$1,052.00