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	$79.42	8.380%	$86.0754	$86.08	$86.10	$86.10
Purchase #2	$202.79	12.845%	$228.8384	$228.84	$228.85	$228.80
Purchase #3	$185.65	4.472%	$193.9523	$193.95	$193.95	$194.00
Purchase #4	$237.64	11.320%	$264.5408	$264.54	$264.55	$264.50
Purchase #5	$82.60	5.249%	$86.9357	$86.94	$86.95	$86.90
Purchase #6	$53.45	11.117%	$59.392	$59.39	$59.40	$59.40
Purchase #7	$78.58	13.151%	$88.9141	$88.91	$88.90	$88.90
7 purchase totals =	$920.13		$1,008.6487	$1,008.65	$1,008.70	$1,008.60