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	$169.53	5.462%	$178.7897	$178.79	$178.80	$178.80
Purchase #2	$124.50	13.547%	$141.366	$141.37	$141.35	$141.40
Purchase #3	$133.68	10.544%	$147.7752	$147.78	$147.80	$147.80
Purchase #4	$205.32	12.525%	$231.0363	$231.04	$231.05	$231.00
Purchase #5	$79.32	13.710%	$90.1948	$90.19	$90.20	$90.20
Purchase #6	$141.27	10.322%	$155.8519	$155.85	$155.85	$155.90
Purchase #7	$65.61	7.274%	$70.3825	$70.38	$70.40	$70.40
7 purchase totals =	$919.23		$1,015.3964	$1,015.40	$1,015.45	$1,015.50