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	$54.65	10.204%	$60.2265	$60.23	$60.25	$60.20
Purchase #2	$186.90	4.146%	$194.6489	$194.65	$194.65	$194.60
Purchase #3	$118.46	11.851%	$132.4987	$132.50	$132.50	$132.50
Purchase #4	$76.39	13.223%	$86.491	$86.49	$86.50	$86.50
Purchase #5	$17.45	7.392%	$18.7399	$18.74	$18.75	$18.70
Purchase #6	$46.28	13.536%	$52.5445	$52.54	$52.55	$52.50
Purchase #7	$158.72	10.813%	$175.8824	$175.88	$175.90	$175.90
7 purchase totals =	$658.85		$721.0319	$721.03	$721.10	$720.90