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	$84.82	6.298%	$90.162	$90.16	$90.15	$90.20
Purchase #2	$45.30	6.503%	$48.2459	$48.25	$48.25	$48.20
Purchase #3	$228.39	6.105%	$242.3332	$242.33	$242.35	$242.30
Purchase #4	$45.69	3.158%	$47.1329	$47.13	$47.15	$47.10
Purchase #5	$38.41	10.312%	$42.3708	$42.37	$42.35	$42.40
Purchase #6	$83.65	7.776%	$90.1546	$90.15	$90.15	$90.20
Purchase #7	$141.34	4.534%	$147.7484	$147.75	$147.75	$147.70
7 purchase totals =	$667.60		$708.1478	$708.14	$708.15	$708.10