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	$108.86	5.560%	$114.9126	$114.91	$114.90	$114.90
Purchase #2	$85.28	6.109%	$90.4898	$90.49	$90.50	$90.50
Purchase #3	$59.98	10.222%	$66.1112	$66.11	$66.10	$66.10
Purchase #4	$94.60	10.466%	$104.5008	$104.50	$104.50	$104.50
Purchase #5	$84.93	5.117%	$89.2759	$89.28	$89.30	$89.30
Purchase #6	$160.47	11.285%	$178.579	$178.58	$178.60	$178.60
Purchase #7	$136.96	4.694%	$143.3889	$143.39	$143.40	$143.40
7 purchase totals =	$731.08		$787.2582	$787.26	$787.30	$787.30