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	$82.90	6.383%	$88.1915	$88.19	$88.20	$88.20
Purchase #2	$212.61	12.328%	$238.8206	$238.82	$238.80	$238.80
Purchase #3	$85.39	5.704%	$90.2606	$90.26	$90.25	$90.30
Purchase #4	$20.51	5.811%	$21.7018	$21.70	$21.70	$21.70
Purchase #5	$68.78	8.466%	$74.6029	$74.60	$74.60	$74.60
Purchase #6	$53.27	12.227%	$59.7833	$59.78	$59.80	$59.80
Purchase #7	$220.87	11.296%	$245.8195	$245.82	$245.80	$245.80
7 purchase totals =	$744.33		$819.1802	$819.17	$819.15	$819.20