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	$214.42	12.679%	$241.6063	$241.61	$241.60	$241.60
Purchase #2	$78.41	6.133%	$83.2189	$83.22	$83.20	$83.20
Purchase #3	$24.90	10.600%	$27.5394	$27.54	$27.55	$27.50
Purchase #4	$121.60	8.468%	$131.8971	$131.90	$131.90	$131.90
Purchase #5	$161.73	11.135%	$179.7386	$179.74	$179.75	$179.70
Purchase #6	$99.52	9.446%	$108.9207	$108.92	$108.90	$108.90
Purchase #7	$119.69	4.754%	$125.3801	$125.38	$125.40	$125.40
7 purchase totals =	$820.27		$898.3011	$898.31	$898.30	$898.20