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	$40.65	9.310%	$44.4345	$44.43	$44.45	$44.40
Purchase #2	$155.97	6.830%	$166.6228	$166.62	$166.60	$166.60
Purchase #3	$158.89	13.520%	$180.3719	$180.37	$180.35	$180.40
Purchase #4	$43.50	11.278%	$48.4059	$48.41	$48.40	$48.40
Purchase #5	$165.40	8.534%	$179.5152	$179.52	$179.50	$179.50
Purchase #6	$112.46	3.676%	$116.594	$116.59	$116.60	$116.60
Purchase #7	$139.53	8.642%	$151.5882	$151.59	$151.60	$151.60
7 purchase totals =	$816.40		$887.5325	$887.53	$887.50	$887.50