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	$143.84	10.466%	$158.8943	$158.89	$158.90	$158.90
Purchase #2	$131.65	7.827%	$141.9542	$141.95	$141.95	$142.00
Purchase #3	$27.28	11.740%	$30.4827	$30.48	$30.50	$30.50
Purchase #4	$32.47	4.218%	$33.8396	$33.84	$33.85	$33.80
Purchase #5	$234.62	6.506%	$249.8844	$249.88	$249.90	$249.90
Purchase #6	$159.47	3.733%	$165.423	$165.42	$165.40	$165.40
Purchase #7	$83.55	6.246%	$88.7685	$88.77	$88.75	$88.80
7 purchase totals =	$812.88		$869.2467	$869.23	$869.25	$869.30