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	$250.84	11.856%	$280.5796	$280.58	$280.60	$280.60
Purchase #2	$27.33	4.796%	$28.6407	$28.64	$28.65	$28.60
Purchase #3	$96.86	3.330%	$100.0854	$100.09	$100.10	$100.10
Purchase #4	$15.94	13.266%	$18.0546	$18.05	$18.05	$18.10
Purchase #5	$82.82	9.586%	$90.7591	$90.76	$90.75	$90.80
Purchase #6	$176.54	9.222%	$192.8205	$192.82	$192.80	$192.80
Purchase #7	$56.64	8.183%	$61.2749	$61.27	$61.25	$61.30
7 purchase totals =	$706.97		$772.2148	$772.21	$772.20	$772.30