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	$15.49	7.778%	$16.6948	$16.69	$16.70	$16.70
Purchase #2	$181.52	4.609%	$189.8863	$189.89	$189.90	$189.90
Purchase #3	$98.41	12.844%	$111.0498	$111.05	$111.05	$111.00
Purchase #4	$53.66	4.795%	$56.233	$56.23	$56.25	$56.20
Purchase #5	$19.81	11.362%	$22.0608	$22.06	$22.05	$22.10
Purchase #6	$56.97	4.215%	$59.3713	$59.37	$59.35	$59.40
Purchase #7	$58.76	13.341%	$66.5992	$66.60	$66.60	$66.60
7 purchase totals =	$484.62		$521.8952	$521.89	$521.90	$521.90