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	$18.87	6.622%	$20.1196	$20.12	$20.10	$20.10
Purchase #2	$78.48	11.260%	$87.3168	$87.32	$87.30	$87.30
Purchase #3	$118.58	10.586%	$131.1329	$131.13	$131.15	$131.10
Purchase #4	$206.26	13.761%	$234.6434	$234.64	$234.65	$234.60
Purchase #5	$164.86	5.759%	$174.3543	$174.35	$174.35	$174.40
Purchase #6	$127.76	12.177%	$143.3173	$143.32	$143.30	$143.30
Purchase #7	$133.43	8.295%	$144.498	$144.50	$144.50	$144.50
7 purchase totals =	$848.24		$935.3823	$935.38	$935.35	$935.30