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	$47.95	12.610%	$53.9965	$54.00	$54.00	$54.00
Purchase #2	$142.69	5.228%	$150.1498	$150.15	$150.15	$150.10
Purchase #3	$80.33	6.146%	$85.2671	$85.27	$85.25	$85.30
Purchase #4	$107.72	4.589%	$112.6633	$112.66	$112.65	$112.70
Purchase #5	$44.84	13.466%	$50.8782	$50.88	$50.90	$50.90
Purchase #6	$132.87	9.688%	$145.7424	$145.74	$145.75	$145.70
Purchase #7	$223.78	3.537%	$231.6951	$231.70	$231.70	$231.70
7 purchase totals =	$780.18		$830.3924	$830.40	$830.40	$830.40