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	$118.61	3.792%	$123.1077	$123.11	$123.10	$123.10
Purchase #2	$178.36	12.205%	$200.1288	$200.13	$200.15	$200.10
Purchase #3	$108.66	4.128%	$113.1455	$113.15	$113.15	$113.10
Purchase #4	$79.78	8.844%	$86.8357	$86.84	$86.85	$86.80
Purchase #5	$225.49	9.532%	$246.9837	$246.98	$247.00	$247.00
Purchase #6	$31.26	9.680%	$34.286	$34.29	$34.30	$34.30
Purchase #7	$40.71	5.310%	$42.8717	$42.87	$42.85	$42.90
7 purchase totals =	$782.87		$847.3591	$847.37	$847.40	$847.30