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	$134.89	7.555%	$145.0809	$145.08	$145.10	$145.10
Purchase #2	$38.47	4.698%	$40.2773	$40.28	$40.30	$40.30
Purchase #3	$216.57	8.192%	$234.3114	$234.31	$234.30	$234.30
Purchase #4	$99.62	12.276%	$111.8494	$111.85	$111.85	$111.80
Purchase #5	$183.97	4.286%	$191.855	$191.86	$191.85	$191.90
Purchase #6	$237.81	7.459%	$255.5482	$255.55	$255.55	$255.50
Purchase #7	$142.97	11.791%	$159.8276	$159.83	$159.85	$159.80
7 purchase totals =	$1,054.30		$1,138.7498	$1,138.76	$1,138.80	$1,138.70