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	$57.98	6.670%	$61.8473	$61.85	$61.85	$61.80
Purchase #2	$36.84	13.734%	$41.8996	$41.90	$41.90	$41.90
Purchase #3	$154.64	11.752%	$172.8133	$172.81	$172.80	$172.80
Purchase #4	$40.45	4.205%	$42.1509	$42.15	$42.15	$42.20
Purchase #5	$83.52	10.577%	$92.3539	$92.35	$92.35	$92.40
Purchase #6	$236.64	5.674%	$250.067	$250.07	$250.05	$250.10
Purchase #7	$6.98	11.271%	$7.7667	$7.77	$7.75	$7.80
7 purchase totals =	$617.05		$668.8987	$668.90	$668.85	$669.00