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	$123.93	9.512%	$135.7182	$135.72	$135.70	$135.70
Purchase #2	$161.46	6.845%	$172.5119	$172.51	$172.50	$172.50
Purchase #3	$11.37	10.644%	$12.5802	$12.58	$12.60	$12.60
Purchase #4	$133.71	4.303%	$139.4635	$139.46	$139.45	$139.50
Purchase #5	$60.81	7.599%	$65.431	$65.43	$65.45	$65.40
Purchase #6	$59.69	10.322%	$65.8512	$65.85	$65.85	$65.90
Purchase #7	$27.53	3.356%	$28.4539	$28.45	$28.45	$28.50
7 purchase totals =	$578.50		$620.0099	$620.00	$620.00	$620.10