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	$33.40	8.319%	$36.1785	$36.18	$36.20	$36.20
Purchase #2	$55.27	5.445%	$58.2795	$58.28	$58.30	$58.30
Purchase #3	$10.63	11.853%	$11.89	$11.89	$11.90	$11.90
Purchase #4	$81.48	9.854%	$89.509	$89.51	$89.50	$89.50
Purchase #5	$61.70	9.546%	$67.5899	$67.59	$67.60	$67.60
Purchase #6	$83.78	6.495%	$89.2215	$89.22	$89.20	$89.20
Purchase #7	$74.88	9.862%	$82.2647	$82.26	$82.25	$82.30
7 purchase totals =	$401.14		$434.9331	$434.93	$434.95	$435.00