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	$229.79	12.679%	$258.9251	$258.93	$258.95	$258.90
Purchase #2	$179.89	4.446%	$187.8879	$187.89	$187.90	$187.90
Purchase #3	$26.60	6.257%	$28.2644	$28.26	$28.25	$28.30
Purchase #4	$99.75	8.595%	$108.3235	$108.32	$108.30	$108.30
Purchase #5	$18.83	10.792%	$20.8621	$20.86	$20.85	$20.90
Purchase #6	$165.40	5.335%	$174.2241	$174.22	$174.20	$174.20
Purchase #7	$130.33	3.139%	$134.4211	$134.42	$134.40	$134.40
7 purchase totals =	$850.59		$912.9082	$912.90	$912.85	$912.90