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	$53.83	13.504%	$61.0992	$61.10	$61.10	$61.10
Purchase #2	$212.60	10.261%	$234.4149	$234.41	$234.40	$234.40
Purchase #3	$222.52	5.339%	$234.4003	$234.40	$234.40	$234.40
Purchase #4	$78.40	5.256%	$82.5207	$82.52	$82.50	$82.50
Purchase #5	$247.75	12.351%	$278.3496	$278.35	$278.35	$278.30
Purchase #6	$207.25	4.678%	$216.9452	$216.95	$216.95	$216.90
Purchase #7	$215.79	6.167%	$229.0978	$229.10	$229.10	$229.10
7 purchase totals =	$1,238.14		$1,336.8277	$1,336.83	$1,336.80	$1,336.70