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	$55.56	6.622%	$59.2392	$59.24	$59.25	$59.20
Purchase #2	$239.63	5.437%	$252.6587	$252.66	$252.65	$252.70
Purchase #3	$119.60	3.235%	$123.4691	$123.47	$123.45	$123.50
Purchase #4	$205.31	7.484%	$220.6754	$220.68	$220.70	$220.70
Purchase #5	$30.72	5.780%	$32.4956	$32.50	$32.50	$32.50
Purchase #6	$176.47	10.613%	$195.1988	$195.20	$195.20	$195.20
Purchase #7	$85.56	10.571%	$94.6045	$94.60	$94.60	$94.60
7 purchase totals =	$912.85		$978.3413	$978.35	$978.35	$978.40