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	$103.49	13.774%	$117.7447	$117.74	$117.75	$117.70
Purchase #2	$191.68	10.175%	$211.1834	$211.18	$211.20	$211.20
Purchase #3	$102.81	10.474%	$113.5783	$113.58	$113.60	$113.60
Purchase #4	$150.90	13.483%	$171.2458	$171.25	$171.25	$171.20
Purchase #5	$48.62	5.152%	$51.1249	$51.12	$51.10	$51.10
Purchase #6	$123.39	13.417%	$139.9452	$139.95	$139.95	$139.90
Purchase #7	$94.44	6.434%	$100.5163	$100.52	$100.50	$100.50
7 purchase totals =	$815.33		$905.3386	$905.34	$905.35	$905.20