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	$150.55	13.770%	$171.2807	$171.28	$171.30	$171.30
Purchase #2	$163.55	11.128%	$181.7498	$181.75	$181.75	$181.70
Purchase #3	$54.61	10.760%	$60.486	$60.49	$60.50	$60.50
Purchase #4	$69.93	12.104%	$78.3943	$78.39	$78.40	$78.40
Purchase #5	$112.45	7.427%	$120.8017	$120.80	$120.80	$120.80
Purchase #6	$10.60	4.164%	$11.0414	$11.04	$11.05	$11.00
Purchase #7	$215.92	13.225%	$244.4754	$244.48	$244.50	$244.50
7 purchase totals =	$777.61		$868.2293	$868.23	$868.30	$868.20