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	$21.59	12.506%	$24.29	$24.29	$24.30	$24.30
Purchase #2	$97.25	7.301%	$104.3502	$104.35	$104.35	$104.40
Purchase #3	$115.52	6.788%	$123.3615	$123.36	$123.35	$123.40
Purchase #4	$77.48	5.214%	$81.5198	$81.52	$81.50	$81.50
Purchase #5	$168.31	13.864%	$191.6445	$191.64	$191.65	$191.60
Purchase #6	$75.58	3.386%	$78.1391	$78.14	$78.15	$78.10
Purchase #7	$17.81	10.488%	$19.6779	$19.68	$19.70	$19.70
7 purchase totals =	$573.54		$622.9830	$622.98	$623.00	$623.00