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	$157.77	9.266%	$172.389	$172.39	$172.40	$172.40
Purchase #2	$54.36	3.228%	$56.1147	$56.11	$56.10	$56.10
Purchase #3	$33.30	4.860%	$34.9184	$34.92	$34.90	$34.90
Purchase #4	$168.94	6.456%	$179.8468	$179.85	$179.85	$179.80
Purchase #5	$37.96	10.656%	$42.005	$42.01	$42.00	$42.00
Purchase #6	$242.89	7.250%	$260.4995	$260.50	$260.50	$260.50
Purchase #7	$18.25	5.102%	$19.1811	$19.18	$19.20	$19.20
7 purchase totals =	$713.47		$764.9545	$764.96	$764.95	$764.90