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	$31.35	9.659%	$34.3781	$34.38	$34.40	$34.40
Purchase #2	$30.99	5.364%	$32.6523	$32.65	$32.65	$32.70
Purchase #3	$42.26	6.714%	$45.0973	$45.10	$45.10	$45.10
Purchase #4	$160.41	6.707%	$171.1687	$171.17	$171.15	$171.20
Purchase #5	$59.97	7.500%	$64.4678	$64.47	$64.45	$64.50
Purchase #6	$84.47	6.466%	$89.9318	$89.93	$89.95	$89.90
Purchase #7	$139.50	8.372%	$151.1789	$151.18	$151.20	$151.20
7 purchase totals =	$548.95		$588.8749	$588.88	$588.90	$589.00