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	$123.75	4.337%	$129.117	$129.12	$129.10	$129.10
Purchase #2	$36.55	13.121%	$41.3457	$41.35	$41.35	$41.30
Purchase #3	$78.30	12.597%	$88.1635	$88.16	$88.15	$88.20
Purchase #4	$84.80	6.671%	$90.457	$90.46	$90.45	$90.50
Purchase #5	$228.50	12.812%	$257.7754	$257.78	$257.80	$257.80
Purchase #6	$92.89	13.768%	$105.6791	$105.68	$105.70	$105.70
Purchase #7	$170.25	9.105%	$185.7513	$185.75	$185.75	$185.80
7 purchase totals =	$815.04		$898.2890	$898.30	$898.30	$898.40