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	$19.68	7.484%	$21.1529	$21.15	$21.15	$21.20
Purchase #2	$212.77	10.795%	$235.7385	$235.74	$235.75	$235.70
Purchase #3	$144.46	12.491%	$162.5045	$162.50	$162.50	$162.50
Purchase #4	$52.25	13.644%	$59.379	$59.38	$59.40	$59.40
Purchase #5	$128.69	3.292%	$132.9265	$132.93	$132.95	$132.90
Purchase #6	$99.67	12.869%	$112.4965	$112.50	$112.50	$112.50
Purchase #7	$128.81	5.786%	$136.2629	$136.26	$136.25	$136.30
7 purchase totals =	$786.33		$860.4608	$860.46	$860.50	$860.50