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	$234.47	6.680%	$250.1326	$250.13	$250.15	$250.10
Purchase #2	$81.50	11.783%	$91.1031	$91.10	$91.10	$91.10
Purchase #3	$189.25	13.442%	$214.689	$214.69	$214.70	$214.70
Purchase #4	$70.43	4.505%	$73.6029	$73.60	$73.60	$73.60
Purchase #5	$14.77	12.332%	$16.5914	$16.59	$16.60	$16.60
Purchase #6	$208.35	3.623%	$215.8985	$215.90	$215.90	$215.90
Purchase #7	$110.94	7.725%	$119.5101	$119.51	$119.50	$119.50
7 purchase totals =	$909.71		$981.5276	$981.52	$981.55	$981.50