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	$49.91	10.282%	$55.0417	$55.04	$55.05	$55.00
Purchase #2	$65.88	3.146%	$67.9526	$67.95	$67.95	$68.00
Purchase #3	$77.60	9.547%	$85.0085	$85.01	$85.00	$85.00
Purchase #4	$46.91	5.602%	$49.5379	$49.54	$49.55	$49.50
Purchase #5	$62.85	3.330%	$64.9429	$64.94	$64.95	$64.90
Purchase #6	$19.72	9.615%	$21.6161	$21.62	$21.60	$21.60
Purchase #7	$81.39	9.532%	$89.1481	$89.15	$89.15	$89.10
7 purchase totals =	$404.26		$433.2478	$433.25	$433.25	$433.10