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	$103.89	5.587%	$109.6943	$109.69	$109.70	$109.70
Purchase #2	$37.27	13.628%	$42.3492	$42.35	$42.35	$42.30
Purchase #3	$126.49	12.671%	$142.5175	$142.52	$142.50	$142.50
Purchase #4	$149.41	3.270%	$154.2957	$154.30	$154.30	$154.30
Purchase #5	$51.39	10.477%	$56.7741	$56.77	$56.75	$56.80
Purchase #6	$167.46	8.189%	$181.1733	$181.17	$181.15	$181.20
Purchase #7	$179.64	4.158%	$187.1094	$187.11	$187.10	$187.10
7 purchase totals =	$815.55		$873.9135	$873.91	$873.85	$873.90