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	$74.93	5.163%	$78.7986	$78.80	$78.80	$78.80
Purchase #2	$140.52	10.799%	$155.6948	$155.69	$155.70	$155.70
Purchase #3	$37.71	10.518%	$41.6763	$41.68	$41.70	$41.70
Purchase #4	$67.41	7.333%	$72.3532	$72.35	$72.35	$72.40
Purchase #5	$41.60	9.556%	$45.5753	$45.58	$45.60	$45.60
Purchase #6	$150.89	3.147%	$155.6385	$155.64	$155.65	$155.60
Purchase #7	$68.28	13.669%	$77.6132	$77.61	$77.60	$77.60
7 purchase totals =	$581.34		$627.3499	$627.35	$627.40	$627.40