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	$73.51	6.570%	$78.3396	$78.34	$78.35	$78.30
Purchase #2	$216.83	6.314%	$230.5206	$230.52	$230.50	$230.50
Purchase #3	$168.55	13.140%	$190.6975	$190.70	$190.70	$190.70
Purchase #4	$75.79	5.282%	$79.7932	$79.79	$79.80	$79.80
Purchase #5	$181.74	8.190%	$196.6245	$196.62	$196.60	$196.60
Purchase #6	$124.89	10.797%	$138.3744	$138.37	$138.35	$138.40
Purchase #7	$53.94	5.414%	$56.8603	$56.86	$56.85	$56.90
7 purchase totals =	$895.25		$971.2101	$971.20	$971.15	$971.20