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	$184.93	12.678%	$208.3754	$208.38	$208.40	$208.40
Purchase #2	$127.74	13.460%	$144.9338	$144.93	$144.95	$144.90
Purchase #3	$50.32	5.170%	$52.9215	$52.92	$52.90	$52.90
Purchase #4	$78.32	6.254%	$83.2181	$83.22	$83.20	$83.20
Purchase #5	$204.99	5.173%	$215.5941	$215.59	$215.60	$215.60
Purchase #6	$57.91	13.409%	$65.6752	$65.68	$65.70	$65.70
Purchase #7	$62.90	11.559%	$70.1706	$70.17	$70.15	$70.20
7 purchase totals =	$767.11		$840.8887	$840.89	$840.90	$840.90