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	$132.97	13.124%	$150.421	$150.42	$150.40	$150.40
Purchase #2	$119.74	10.217%	$131.9738	$131.97	$131.95	$132.00
Purchase #3	$151.64	13.547%	$172.1827	$172.18	$172.20	$172.20
Purchase #4	$93.78	7.411%	$100.73	$100.73	$100.75	$100.70
Purchase #5	$24.78	11.604%	$27.6555	$27.66	$27.65	$27.70
Purchase #6	$56.99	4.121%	$59.3386	$59.34	$59.35	$59.30
Purchase #7	$14.58	6.194%	$15.4831	$15.48	$15.50	$15.50
7 purchase totals =	$594.48		$657.7847	$657.78	$657.80	$657.80