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	$138.33	13.417%	$156.8897	$156.89	$156.90	$156.90
Purchase #2	$70.99	10.522%	$78.4596	$78.46	$78.45	$78.50
Purchase #3	$222.28	12.724%	$250.5629	$250.56	$250.55	$250.60
Purchase #4	$108.51	9.592%	$118.9183	$118.92	$118.90	$118.90
Purchase #5	$138.64	8.331%	$150.1901	$150.19	$150.20	$150.20
Purchase #6	$124.97	6.205%	$132.7244	$132.72	$132.70	$132.70
Purchase #7	$247.25	8.298%	$267.7668	$267.77	$267.75	$267.80
7 purchase totals =	$1,050.97		$1,155.5118	$1,155.51	$1,155.45	$1,155.60