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	$51.86	5.303%	$54.6101	$54.61	$54.60	$54.60
Purchase #2	$70.47	11.712%	$78.7234	$78.72	$78.70	$78.70
Purchase #3	$90.52	7.494%	$97.3036	$97.30	$97.30	$97.30
Purchase #4	$133.72	7.394%	$143.6073	$143.61	$143.60	$143.60
Purchase #5	$39.91	3.721%	$41.3951	$41.40	$41.40	$41.40
Purchase #6	$50.29	4.572%	$52.5893	$52.59	$52.60	$52.60
Purchase #7	$85.81	12.641%	$96.6572	$96.66	$96.65	$96.70
7 purchase totals =	$522.58		$564.8860	$564.89	$564.85	$564.90