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	$10.84	12.803%	$12.2278	$12.23	$12.25	$12.20
Purchase #2	$152.83	10.510%	$168.8924	$168.89	$168.90	$168.90
Purchase #3	$120.89	5.504%	$127.5438	$127.54	$127.55	$127.50
Purchase #4	$168.25	10.699%	$186.2511	$186.25	$186.25	$186.30
Purchase #5	$16.55	8.701%	$17.99	$17.99	$18.00	$18.00
Purchase #6	$41.81	10.375%	$46.1478	$46.15	$46.15	$46.10
Purchase #7	$99.90	8.439%	$108.3306	$108.33	$108.35	$108.30
7 purchase totals =	$611.07		$667.3835	$667.38	$667.45	$667.30