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	$65.89	13.697%	$74.915	$74.92	$74.90	$74.90
Purchase #2	$147.33	8.205%	$159.4184	$159.42	$159.40	$159.40
Purchase #3	$68.45	6.866%	$73.1498	$73.15	$73.15	$73.10
Purchase #4	$44.72	12.294%	$50.2179	$50.22	$50.20	$50.20
Purchase #5	$117.79	8.233%	$127.4877	$127.49	$127.50	$127.50
Purchase #6	$74.69	5.442%	$78.7546	$78.75	$78.75	$78.80
Purchase #7	$219.94	13.383%	$249.3746	$249.37	$249.35	$249.40
7 purchase totals =	$738.81		$813.3180	$813.32	$813.25	$813.30