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	$98.70	9.584%	$108.1594	$108.16	$108.15	$108.20
Purchase #2	$167.70	10.591%	$185.4611	$185.46	$185.45	$185.50
Purchase #3	$104.52	13.653%	$118.7901	$118.79	$118.80	$118.80
Purchase #4	$208.68	9.250%	$227.9829	$227.98	$228.00	$228.00
Purchase #5	$45.93	5.277%	$48.3537	$48.35	$48.35	$48.40
Purchase #6	$168.86	9.658%	$185.1685	$185.17	$185.15	$185.20
Purchase #7	$93.32	10.427%	$103.0505	$103.05	$103.05	$103.10
7 purchase totals =	$887.71		$976.9662	$976.96	$976.95	$977.20