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	$134.77	6.712%	$143.8158	$143.82	$143.80	$143.80
Purchase #2	$106.30	5.577%	$112.2284	$112.23	$112.25	$112.20
Purchase #3	$249.44	10.258%	$275.0276	$275.03	$275.05	$275.00
Purchase #4	$108.36	6.516%	$115.4207	$115.42	$115.40	$115.40
Purchase #5	$179.50	9.333%	$196.2527	$196.25	$196.25	$196.30
Purchase #6	$42.88	12.455%	$48.2207	$48.22	$48.20	$48.20
Purchase #7	$149.64	5.698%	$158.1665	$158.17	$158.15	$158.20
7 purchase totals =	$970.89		$1,049.1324	$1,049.14	$1,049.10	$1,049.10