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	$170.50	5.533%	$179.9338	$179.93	$179.95	$179.90
Purchase #2	$87.73	4.449%	$91.6331	$91.63	$91.65	$91.60
Purchase #3	$130.71	11.564%	$145.8253	$145.83	$145.85	$145.80
Purchase #4	$52.98	12.539%	$59.6232	$59.62	$59.60	$59.60
Purchase #5	$34.66	7.768%	$37.3524	$37.35	$37.35	$37.40
Purchase #6	$121.34	5.784%	$128.3583	$128.36	$128.35	$128.40
Purchase #7	$172.84	6.154%	$183.4766	$183.48	$183.50	$183.50
7 purchase totals =	$770.76		$826.2027	$826.20	$826.25	$826.20