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	$89.28	12.601%	$100.5302	$100.53	$100.55	$100.50
Purchase #2	$190.95	12.624%	$215.0555	$215.06	$215.05	$215.10
Purchase #3	$127.93	10.696%	$141.6134	$141.61	$141.60	$141.60
Purchase #4	$122.99	9.466%	$134.6322	$134.63	$134.65	$134.60
Purchase #5	$75.68	4.637%	$79.1893	$79.19	$79.20	$79.20
Purchase #6	$72.91	7.440%	$78.3345	$78.33	$78.35	$78.30
Purchase #7	$231.34	4.273%	$241.2252	$241.23	$241.25	$241.20
7 purchase totals =	$911.08		$990.5803	$990.58	$990.65	$990.50