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	$249.90	6.346%	$265.7587	$265.76	$265.75	$265.80
Purchase #2	$152.91	10.267%	$168.6093	$168.61	$168.60	$168.60
Purchase #3	$53.59	7.686%	$57.7089	$57.71	$57.70	$57.70
Purchase #4	$124.64	12.723%	$140.4979	$140.50	$140.50	$140.50
Purchase #5	$41.62	5.563%	$43.9353	$43.94	$43.95	$43.90
Purchase #6	$136.35	13.253%	$154.4205	$154.42	$154.40	$154.40
Purchase #7	$158.74	11.869%	$177.5809	$177.58	$177.60	$177.60
7 purchase totals =	$917.75		$1,008.5115	$1,008.52	$1,008.50	$1,008.50