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	$208.57	10.359%	$230.1758	$230.18	$230.20	$230.20
Purchase #2	$105.77	6.510%	$112.6556	$112.66	$112.65	$112.70
Purchase #3	$87.68	9.367%	$95.893	$95.89	$95.90	$95.90
Purchase #4	$104.32	10.400%	$115.1693	$115.17	$115.15	$115.20
Purchase #5	$81.89	10.258%	$90.2903	$90.29	$90.30	$90.30
Purchase #6	$42.84	10.710%	$47.4282	$47.43	$47.45	$47.40
Purchase #7	$179.86	3.240%	$185.6875	$185.69	$185.70	$185.70
7 purchase totals =	$810.93		$877.2997	$877.31	$877.35	$877.40