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	$60.73	6.160%	$64.471	$64.47	$64.45	$64.50
Purchase #2	$28.51	4.284%	$29.7314	$29.73	$29.75	$29.70
Purchase #3	$172.74	8.777%	$187.9014	$187.90	$187.90	$187.90
Purchase #4	$23.98	13.280%	$27.1645	$27.16	$27.15	$27.20
Purchase #5	$52.67	7.562%	$56.6529	$56.65	$56.65	$56.70
Purchase #6	$34.72	7.239%	$37.2334	$37.23	$37.25	$37.20
Purchase #7	$148.92	12.432%	$167.4337	$167.43	$167.45	$167.40
7 purchase totals =	$522.27		$570.5883	$570.57	$570.60	$570.60