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	$51.89	5.307%	$54.6438	$54.64	$54.65	$54.60
Purchase #2	$137.46	10.245%	$151.5428	$151.54	$151.55	$151.50
Purchase #3	$90.43	11.528%	$100.8548	$100.85	$100.85	$100.90
Purchase #4	$56.78	10.354%	$62.659	$62.66	$62.65	$62.70
Purchase #5	$156.25	7.427%	$167.8547	$167.85	$167.85	$167.90
Purchase #6	$113.44	4.402%	$118.4336	$118.43	$118.45	$118.40
Purchase #7	$157.46	5.489%	$166.103	$166.10	$166.10	$166.10
7 purchase totals =	$763.71		$822.0917	$822.07	$822.10	$822.10