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	$51.74	7.661%	$55.7038	$55.70	$55.70	$55.70
Purchase #2	$89.89	3.298%	$92.8546	$92.85	$92.85	$92.90
Purchase #3	$50.64	10.324%	$55.8681	$55.87	$55.85	$55.90
Purchase #4	$71.90	10.551%	$79.4862	$79.49	$79.50	$79.50
Purchase #5	$180.29	5.693%	$190.5539	$190.55	$190.55	$190.60
Purchase #6	$241.44	9.676%	$264.8017	$264.80	$264.80	$264.80
Purchase #7	$66.64	5.184%	$70.0946	$70.09	$70.10	$70.10
7 purchase totals =	$752.54		$809.3629	$809.35	$809.35	$809.50