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	$18.61	13.482%	$21.119	$21.12	$21.10	$21.10
Purchase #2	$47.72	7.716%	$51.4021	$51.40	$51.40	$51.40
Purchase #3	$140.39	7.615%	$151.0807	$151.08	$151.10	$151.10
Purchase #4	$139.83	12.183%	$156.8655	$156.87	$156.85	$156.90
Purchase #5	$227.42	12.343%	$255.4905	$255.49	$255.50	$255.50
Purchase #6	$164.84	11.743%	$184.1972	$184.20	$184.20	$184.20
Purchase #7	$199.64	12.438%	$224.4712	$224.47	$224.45	$224.50
7 purchase totals =	$938.45		$1,044.6262	$1,044.63	$1,044.60	$1,044.70