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	$105.71	7.244%	$113.3676	$113.37	$113.35	$113.40
Purchase #2	$40.81	11.575%	$45.5338	$45.53	$45.55	$45.50
Purchase #3	$124.32	9.525%	$136.1615	$136.16	$136.15	$136.20
Purchase #4	$75.53	10.354%	$83.3504	$83.35	$83.35	$83.40
Purchase #5	$96.91	11.302%	$107.8628	$107.86	$107.85	$107.90
Purchase #6	$195.45	11.246%	$217.4303	$217.43	$217.45	$217.40
Purchase #7	$121.51	4.750%	$127.2817	$127.28	$127.30	$127.30
7 purchase totals =	$760.24		$830.9881	$830.98	$831.00	$831.10