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	$64.57	3.698%	$66.9578	$66.96	$66.95	$67.00
Purchase #2	$164.62	4.745%	$172.4312	$172.43	$172.45	$172.40
Purchase #3	$50.80	12.265%	$57.0306	$57.03	$57.05	$57.00
Purchase #4	$242.34	13.820%	$275.8314	$275.83	$275.85	$275.80
Purchase #5	$116.55	5.415%	$122.8612	$122.86	$122.85	$122.90
Purchase #6	$65.42	10.810%	$72.4919	$72.49	$72.50	$72.50
Purchase #7	$225.46	11.280%	$250.8919	$250.89	$250.90	$250.90
7 purchase totals =	$929.76		$1,018.4960	$1,018.49	$1,018.55	$1,018.50