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	$19.88	13.369%	$22.5378	$22.54	$22.55	$22.50
Purchase #2	$52.35	3.705%	$54.2896	$54.29	$54.30	$54.30
Purchase #3	$59.45	10.700%	$65.8112	$65.81	$65.80	$65.80
Purchase #4	$209.78	10.378%	$231.551	$231.55	$231.55	$231.60
Purchase #5	$13.86	7.775%	$14.9376	$14.94	$14.95	$14.90
Purchase #6	$167.99	4.522%	$175.5865	$175.59	$175.60	$175.60
Purchase #7	$85.95	11.184%	$95.5626	$95.56	$95.55	$95.60
7 purchase totals =	$609.26		$660.2763	$660.28	$660.30	$660.30