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	$130.99	10.134%	$144.2645	$144.26	$144.25	$144.30
Purchase #2	$127.87	6.465%	$136.1368	$136.14	$136.15	$136.10
Purchase #3	$88.35	8.171%	$95.5691	$95.57	$95.55	$95.60
Purchase #4	$176.59	5.161%	$185.7038	$185.70	$185.70	$185.70
Purchase #5	$19.49	6.611%	$20.7785	$20.78	$20.80	$20.80
Purchase #6	$211.68	10.871%	$234.6917	$234.69	$234.70	$234.70
Purchase #7	$99.35	11.848%	$111.121	$111.12	$111.10	$111.10
7 purchase totals =	$854.32		$928.2654	$928.26	$928.25	$928.30