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	$234.30	3.284%	$241.9944	$241.99	$242.00	$242.00
Purchase #2	$20.32	7.362%	$21.816	$21.82	$21.80	$21.80
Purchase #3	$168.53	10.162%	$185.656	$185.66	$185.65	$185.70
Purchase #4	$41.64	12.833%	$46.9837	$46.98	$47.00	$47.00
Purchase #5	$47.92	13.749%	$54.5085	$54.51	$54.50	$54.50
Purchase #6	$217.62	11.651%	$242.9749	$242.97	$242.95	$243.00
Purchase #7	$187.93	4.606%	$196.5861	$196.59	$196.60	$196.60
7 purchase totals =	$918.26		$990.5196	$990.52	$990.50	$990.60