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	$27.61	4.546%	$28.8652	$28.87	$28.85	$28.90
Purchase #2	$162.74	5.385%	$171.5035	$171.50	$171.50	$171.50
Purchase #3	$173.73	4.663%	$181.831	$181.83	$181.85	$181.80
Purchase #4	$24.55	8.470%	$26.6294	$26.63	$26.65	$26.60
Purchase #5	$204.86	7.240%	$219.6919	$219.69	$219.70	$219.70
Purchase #6	$83.32	3.110%	$85.9113	$85.91	$85.90	$85.90
Purchase #7	$50.69	6.773%	$54.1232	$54.12	$54.10	$54.10
7 purchase totals =	$727.50		$768.5555	$768.55	$768.55	$768.50