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	$102.89	4.680%	$107.7053	$107.71	$107.70	$107.70
Purchase #2	$26.38	6.756%	$28.1622	$28.16	$28.15	$28.20
Purchase #3	$95.95	7.860%	$103.4917	$103.49	$103.50	$103.50
Purchase #4	$39.55	8.413%	$42.8773	$42.88	$42.90	$42.90
Purchase #5	$18.94	12.432%	$21.2946	$21.29	$21.30	$21.30
Purchase #6	$103.89	13.359%	$117.7687	$117.77	$117.75	$117.80
Purchase #7	$196.82	13.147%	$222.6959	$222.70	$222.70	$222.70
7 purchase totals =	$584.42		$643.9957	$644.00	$644.00	$644.10