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	$32.76	4.144%	$34.1176	$34.12	$34.10	$34.10
Purchase #2	$106.96	11.120%	$118.854	$118.85	$118.85	$118.90
Purchase #3	$70.39	11.462%	$78.4581	$78.46	$78.45	$78.50
Purchase #4	$82.67	8.836%	$89.9747	$89.97	$89.95	$90.00
Purchase #5	$60.69	8.825%	$66.0459	$66.05	$66.05	$66.00
Purchase #6	$182.37	7.467%	$195.9876	$195.99	$196.00	$196.00
Purchase #7	$9.52	5.621%	$10.0551	$10.06	$10.05	$10.10
7 purchase totals =	$545.36		$593.4930	$593.50	$593.45	$593.60