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	$82.28	9.119%	$89.7831	$89.78	$89.80	$89.80
Purchase #2	$117.71	12.247%	$132.1259	$132.13	$132.15	$132.10
Purchase #3	$143.53	11.317%	$159.7733	$159.77	$159.75	$159.80
Purchase #4	$194.76	12.105%	$218.3357	$218.34	$218.35	$218.30
Purchase #5	$59.85	9.441%	$65.5004	$65.50	$65.50	$65.50
Purchase #6	$157.55	3.224%	$162.6294	$162.63	$162.65	$162.60
Purchase #7	$124.30	5.273%	$130.8543	$130.85	$130.85	$130.90
7 purchase totals =	$879.98		$959.0021	$959.00	$959.05	$959.00