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	$41.67	7.279%	$44.7032	$44.70	$44.70	$44.70
Purchase #2	$239.40	13.832%	$272.5138	$272.51	$272.50	$272.50
Purchase #3	$37.82	12.611%	$42.5895	$42.59	$42.60	$42.60
Purchase #4	$112.97	10.298%	$124.6037	$124.60	$124.60	$124.60
Purchase #5	$95.52	4.684%	$99.9942	$99.99	$100.00	$100.00
Purchase #6	$19.51	12.414%	$21.932	$21.93	$21.95	$21.90
Purchase #7	$59.90	3.111%	$61.7635	$61.76	$61.75	$61.80
7 purchase totals =	$606.79		$668.0999	$668.08	$668.10	$668.10