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	$50.51	5.554%	$53.3153	$53.32	$53.30	$53.30
Purchase #2	$60.76	10.173%	$66.9411	$66.94	$66.95	$66.90
Purchase #3	$147.32	13.808%	$167.6619	$167.66	$167.65	$167.70
Purchase #4	$7.76	9.384%	$8.4882	$8.49	$8.50	$8.50
Purchase #5	$112.67	8.367%	$122.0971	$122.10	$122.10	$122.10
Purchase #6	$129.88	10.334%	$143.3018	$143.30	$143.30	$143.30
Purchase #7	$99.37	4.520%	$103.8615	$103.86	$103.85	$103.90
7 purchase totals =	$608.27		$665.6669	$665.67	$665.65	$665.70