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	$79.65	13.356%	$90.2881	$90.29	$90.30	$90.30
Purchase #2	$143.84	13.831%	$163.7345	$163.73	$163.75	$163.70
Purchase #3	$71.59	9.792%	$78.6001	$78.60	$78.60	$78.60
Purchase #4	$121.39	5.548%	$128.1247	$128.12	$128.10	$128.10
Purchase #5	$181.71	13.634%	$206.4843	$206.48	$206.50	$206.50
Purchase #6	$232.81	13.616%	$264.5094	$264.51	$264.50	$264.50
Purchase #7	$197.53	8.373%	$214.0692	$214.07	$214.05	$214.10
7 purchase totals =	$1,028.52		$1,145.8103	$1,145.80	$1,145.80	$1,145.80