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	$53.79	11.211%	$59.8204	$59.82	$59.80	$59.80
Purchase #2	$217.57	6.465%	$231.6359	$231.64	$231.65	$231.60
Purchase #3	$249.27	9.457%	$272.8435	$272.84	$272.85	$272.80
Purchase #4	$9.49	9.508%	$10.3923	$10.39	$10.40	$10.40
Purchase #5	$224.47	7.535%	$241.3838	$241.38	$241.40	$241.40
Purchase #6	$56.59	4.689%	$59.2435	$59.24	$59.25	$59.20
Purchase #7	$204.60	9.840%	$224.7326	$224.73	$224.75	$224.70
7 purchase totals =	$1,015.78		$1,100.0520	$1,100.04	$1,100.10	$1,099.90