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	$30.74	13.510%	$34.893	$34.89	$34.90	$34.90
Purchase #2	$21.40	11.526%	$23.8666	$23.87	$23.85	$23.90
Purchase #3	$55.90	6.837%	$59.7219	$59.72	$59.70	$59.70
Purchase #4	$89.96	8.815%	$97.89	$97.89	$97.90	$97.90
Purchase #5	$71.85	8.522%	$77.9731	$77.97	$77.95	$78.00
Purchase #6	$37.97	13.454%	$43.0785	$43.08	$43.10	$43.10
Purchase #7	$86.43	5.490%	$91.175	$91.18	$91.20	$91.20
7 purchase totals =	$394.25		$428.5981	$428.60	$428.60	$428.70