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	$78.31	9.766%	$85.9578	$85.96	$85.95	$86.00
Purchase #2	$40.48	5.298%	$42.6246	$42.62	$42.60	$42.60
Purchase #3	$171.85	5.462%	$181.2364	$181.24	$181.25	$181.20
Purchase #4	$159.94	11.863%	$178.9137	$178.91	$178.90	$178.90
Purchase #5	$149.80	3.161%	$154.5352	$154.54	$154.55	$154.50
Purchase #6	$114.56	11.221%	$127.4148	$127.41	$127.40	$127.40
Purchase #7	$195.49	12.104%	$219.1521	$219.15	$219.15	$219.20
7 purchase totals =	$910.43		$989.8346	$989.83	$989.80	$989.80