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	$39.45	8.605%	$42.8447	$42.84	$42.85	$42.80
Purchase #2	$112.50	8.874%	$122.4833	$122.48	$122.50	$122.50
Purchase #3	$68.45	6.579%	$72.9533	$72.95	$72.95	$73.00
Purchase #4	$71.42	7.588%	$76.8393	$76.84	$76.85	$76.80
Purchase #5	$50.29	11.114%	$55.8792	$55.88	$55.90	$55.90
Purchase #6	$151.32	4.803%	$158.5879	$158.59	$158.60	$158.60
Purchase #7	$67.68	4.233%	$70.5449	$70.54	$70.55	$70.50
7 purchase totals =	$561.11		$600.1326	$600.12	$600.20	$600.10