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	$157.77	6.671%	$168.2948	$168.29	$168.30	$168.30
Purchase #2	$108.91	5.862%	$115.2943	$115.29	$115.30	$115.30
Purchase #3	$12.92	8.766%	$14.0526	$14.05	$14.05	$14.10
Purchase #4	$83.46	6.874%	$89.197	$89.20	$89.20	$89.20
Purchase #5	$123.59	9.668%	$135.5387	$135.54	$135.55	$135.50
Purchase #6	$100.71	11.184%	$111.9734	$111.97	$111.95	$112.00
Purchase #7	$51.49	4.660%	$53.8894	$53.89	$53.90	$53.90
7 purchase totals =	$638.85		$688.2402	$688.23	$688.25	$688.30