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	$10.29	5.596%	$10.8658	$10.87	$10.85	$10.90
Purchase #2	$18.45	10.616%	$20.4087	$20.41	$20.40	$20.40
Purchase #3	$62.42	7.484%	$67.0915	$67.09	$67.10	$67.10
Purchase #4	$53.73	11.316%	$59.8101	$59.81	$59.80	$59.80
Purchase #5	$237.83	6.809%	$254.0238	$254.02	$254.00	$254.00
Purchase #6	$250.27	8.855%	$272.4314	$272.43	$272.45	$272.40
Purchase #7	$83.25	7.211%	$89.2532	$89.25	$89.25	$89.30
7 purchase totals =	$716.24		$773.8845	$773.88	$773.85	$773.90