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	$96.47	13.525%	$109.5176	$109.52	$109.50	$109.50
Purchase #2	$81.56	13.485%	$92.5584	$92.56	$92.55	$92.60
Purchase #3	$204.76	13.196%	$231.7801	$231.78	$231.80	$231.80
Purchase #4	$19.94	9.666%	$21.8674	$21.87	$21.85	$21.90
Purchase #5	$32.66	6.447%	$34.7656	$34.77	$34.75	$34.80
Purchase #6	$179.63	3.738%	$186.3446	$186.34	$186.35	$186.30
Purchase #7	$30.27	6.770%	$32.3193	$32.32	$32.30	$32.30
7 purchase totals =	$645.29		$709.1530	$709.16	$709.10	$709.20