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	$186.32	12.109%	$208.8815	$208.88	$208.90	$208.90
Purchase #2	$69.85	3.821%	$72.519	$72.52	$72.50	$72.50
Purchase #3	$84.49	12.108%	$94.72	$94.72	$94.70	$94.70
Purchase #4	$244.56	5.574%	$258.1918	$258.19	$258.20	$258.20
Purchase #5	$92.29	12.278%	$103.6214	$103.62	$103.60	$103.60
Purchase #6	$183.39	5.153%	$192.8401	$192.84	$192.85	$192.80
Purchase #7	$53.52	11.454%	$59.6502	$59.65	$59.65	$59.70
7 purchase totals =	$914.42		$990.4240	$990.42	$990.40	$990.40