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	$89.81	10.400%	$99.1502	$99.15	$99.15	$99.20
Purchase #2	$156.77	7.211%	$168.0747	$168.07	$168.05	$168.10
Purchase #3	$121.80	9.514%	$133.3881	$133.39	$133.40	$133.40
Purchase #4	$89.63	6.498%	$95.4542	$95.45	$95.45	$95.50
Purchase #5	$223.25	6.620%	$238.0292	$238.03	$238.05	$238.00
Purchase #6	$123.25	5.543%	$130.0817	$130.08	$130.10	$130.10
Purchase #7	$184.94	3.870%	$192.0972	$192.10	$192.10	$192.10
7 purchase totals =	$989.45		$1,056.2753	$1,056.27	$1,056.30	$1,056.40