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	$17.75	3.255%	$18.3278	$18.33	$18.35	$18.30
Purchase #2	$81.51	5.763%	$86.2074	$86.21	$86.20	$86.20
Purchase #3	$156.94	10.166%	$172.8945	$172.89	$172.90	$172.90
Purchase #4	$18.59	7.857%	$20.0506	$20.05	$20.05	$20.10
Purchase #5	$81.26	11.783%	$90.8349	$90.83	$90.85	$90.80
Purchase #6	$234.33	12.524%	$263.6775	$263.68	$263.70	$263.70
Purchase #7	$248.63	4.270%	$259.2465	$259.25	$259.25	$259.20
7 purchase totals =	$839.01		$911.2392	$911.24	$911.30	$911.20