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	$83.54	7.837%	$90.087	$90.09	$90.10	$90.10
Purchase #2	$56.71	4.536%	$59.2824	$59.28	$59.30	$59.30
Purchase #3	$149.49	10.336%	$164.9413	$164.94	$164.95	$164.90
Purchase #4	$58.66	9.784%	$64.3993	$64.40	$64.40	$64.40
Purchase #5	$27.64	10.318%	$30.4919	$30.49	$30.50	$30.50
Purchase #6	$160.32	3.475%	$165.8911	$165.89	$165.90	$165.90
Purchase #7	$108.81	7.719%	$117.209	$117.21	$117.20	$117.20
7 purchase totals =	$645.17		$692.3020	$692.30	$692.35	$692.30