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	$101.92	10.372%	$112.4911	$112.49	$112.50	$112.50
Purchase #2	$50.71	8.203%	$54.8697	$54.87	$54.85	$54.90
Purchase #3	$239.36	11.349%	$266.525	$266.53	$266.55	$266.50
Purchase #4	$127.58	11.348%	$142.0578	$142.06	$142.05	$142.10
Purchase #5	$30.49	7.752%	$32.8536	$32.85	$32.85	$32.90
Purchase #6	$204.51	6.761%	$218.3369	$218.34	$218.35	$218.30
Purchase #7	$229.57	10.546%	$253.7805	$253.78	$253.80	$253.80
7 purchase totals =	$984.14		$1,080.9146	$1,080.92	$1,080.95	$1,081.00