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	$133.25	6.424%	$141.81	$141.81	$141.80	$141.80
Purchase #2	$139.38	11.746%	$155.7516	$155.75	$155.75	$155.80
Purchase #3	$59.85	12.796%	$67.5084	$67.51	$67.50	$67.50
Purchase #4	$36.83	6.394%	$39.1849	$39.18	$39.20	$39.20
Purchase #5	$38.88	5.110%	$40.8668	$40.87	$40.85	$40.90
Purchase #6	$242.54	13.750%	$275.8893	$275.89	$275.90	$275.90
Purchase #7	$161.77	5.575%	$170.7887	$170.79	$170.80	$170.80
7 purchase totals =	$812.50		$891.7997	$891.80	$891.80	$891.90