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	$49.66	10.570%	$54.9091	$54.91	$54.90	$54.90
Purchase #2	$6.75	10.601%	$7.4656	$7.47	$7.45	$7.50
Purchase #3	$37.64	13.383%	$42.6774	$42.68	$42.70	$42.70
Purchase #4	$19.38	9.626%	$21.2455	$21.25	$21.25	$21.20
Purchase #5	$17.77	6.697%	$18.9601	$18.96	$18.95	$19.00
Purchase #6	$32.81	13.192%	$37.1383	$37.14	$37.15	$37.10
Purchase #7	$231.46	6.496%	$246.4956	$246.50	$246.50	$246.50
7 purchase totals =	$395.47		$428.8916	$428.91	$428.90	$428.90