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	$17.53	4.495%	$18.318	$18.32	$18.30	$18.30
Purchase #2	$187.27	11.150%	$208.1506	$208.15	$208.15	$208.20
Purchase #3	$154.59	12.503%	$173.9184	$173.92	$173.90	$173.90
Purchase #4	$32.90	4.553%	$34.3979	$34.40	$34.40	$34.40
Purchase #5	$57.89	3.507%	$59.9202	$59.92	$59.90	$59.90
Purchase #6	$244.44	3.182%	$252.2181	$252.22	$252.20	$252.20
Purchase #7	$126.63	10.460%	$139.8755	$139.88	$139.90	$139.90
7 purchase totals =	$821.25		$886.7987	$886.81	$886.75	$886.80