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	$96.56	3.206%	$99.6557	$99.66	$99.65	$99.70
Purchase #2	$33.64	10.390%	$37.1352	$37.14	$37.15	$37.10
Purchase #3	$99.46	4.546%	$103.9815	$103.98	$104.00	$104.00
Purchase #4	$100.34	5.529%	$105.8878	$105.89	$105.90	$105.90
Purchase #5	$181.50	9.701%	$199.1073	$199.11	$199.10	$199.10
Purchase #6	$117.30	8.799%	$127.6212	$127.62	$127.60	$127.60
Purchase #7	$15.93	7.465%	$17.1192	$17.12	$17.10	$17.10
7 purchase totals =	$644.73		$690.5079	$690.52	$690.50	$690.50