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	$13.28	4.125%	$13.8278	$13.83	$13.85	$13.80
Purchase #2	$117.52	8.818%	$127.8829	$127.88	$127.90	$127.90
Purchase #3	$205.80	10.261%	$226.9171	$226.92	$226.90	$226.90
Purchase #4	$6.68	9.533%	$7.3168	$7.32	$7.30	$7.30
Purchase #5	$112.89	12.811%	$127.3523	$127.35	$127.35	$127.40
Purchase #6	$83.58	4.440%	$87.291	$87.29	$87.30	$87.30
Purchase #7	$190.87	10.157%	$210.2567	$210.26	$210.25	$210.30
7 purchase totals =	$730.62		$800.8446	$800.85	$800.85	$800.90