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	$247.74	8.536%	$268.8871	$268.89	$268.90	$268.90
Purchase #2	$27.78	9.516%	$30.4235	$30.42	$30.40	$30.40
Purchase #3	$130.52	8.664%	$141.8283	$141.83	$141.85	$141.80
Purchase #4	$57.98	5.319%	$61.064	$61.06	$61.05	$61.10
Purchase #5	$58.68	11.262%	$65.2885	$65.29	$65.30	$65.30
Purchase #6	$223.62	7.405%	$240.1791	$240.18	$240.20	$240.20
Purchase #7	$50.51	6.574%	$53.8305	$53.83	$53.85	$53.80
7 purchase totals =	$796.83		$861.5010	$861.50	$861.55	$861.50