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	$40.31	8.864%	$43.8831	$43.88	$43.90	$43.90
Purchase #2	$109.74	12.802%	$123.7889	$123.79	$123.80	$123.80
Purchase #3	$242.37	3.845%	$251.6891	$251.69	$251.70	$251.70
Purchase #4	$122.36	12.105%	$137.1717	$137.17	$137.15	$137.20
Purchase #5	$141.31	8.312%	$153.0557	$153.06	$153.05	$153.10
Purchase #6	$71.81	11.785%	$80.2728	$80.27	$80.25	$80.30
Purchase #7	$168.59	11.848%	$188.5645	$188.56	$188.55	$188.60
7 purchase totals =	$896.49		$978.4258	$978.42	$978.40	$978.60