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	$72.99	8.156%	$78.9431	$78.94	$78.95	$78.90
Purchase #2	$40.60	11.794%	$45.3884	$45.39	$45.40	$45.40
Purchase #3	$151.59	9.126%	$165.4241	$165.42	$165.40	$165.40
Purchase #4	$97.32	13.657%	$110.611	$110.61	$110.60	$110.60
Purchase #5	$103.29	4.692%	$108.1364	$108.14	$108.15	$108.10
Purchase #6	$241.42	10.111%	$265.83	$265.83	$265.85	$265.80
Purchase #7	$8.89	11.684%	$9.9287	$9.93	$9.95	$9.90
7 purchase totals =	$716.10		$784.2617	$784.26	$784.30	$784.10