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	$101.68	9.719%	$111.5623	$111.56	$111.55	$111.60
Purchase #2	$164.25	3.663%	$170.2665	$170.27	$170.25	$170.30
Purchase #3	$180.66	12.753%	$203.6996	$203.70	$203.70	$203.70
Purchase #4	$78.54	9.305%	$85.8481	$85.85	$85.85	$85.80
Purchase #5	$106.44	5.745%	$112.555	$112.56	$112.55	$112.60
Purchase #6	$208.98	8.102%	$225.9116	$225.91	$225.90	$225.90
Purchase #7	$71.35	13.219%	$80.7818	$80.78	$80.80	$80.80
7 purchase totals =	$911.90		$990.6249	$990.63	$990.60	$990.70