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	$91.93	12.820%	$103.7154	$103.72	$103.70	$103.70
Purchase #2	$95.59	8.213%	$103.4408	$103.44	$103.45	$103.40
Purchase #3	$155.29	6.792%	$165.8373	$165.84	$165.85	$165.80
Purchase #4	$78.79	7.436%	$84.6488	$84.65	$84.65	$84.60
Purchase #5	$94.91	8.835%	$103.2953	$103.30	$103.30	$103.30
Purchase #6	$104.30	6.838%	$111.432	$111.43	$111.45	$111.40
Purchase #7	$155.58	11.598%	$173.6242	$173.62	$173.60	$173.60
7 purchase totals =	$776.39		$845.9938	$846.00	$846.00	$845.80