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	$169.93	12.111%	$190.5102	$190.51	$190.50	$190.50
Purchase #2	$111.82	11.756%	$124.9656	$124.97	$124.95	$125.00
Purchase #3	$95.35	11.188%	$106.0178	$106.02	$106.00	$106.00
Purchase #4	$18.42	11.823%	$20.5978	$20.60	$20.60	$20.60
Purchase #5	$76.59	9.606%	$83.9472	$83.95	$83.95	$83.90
Purchase #6	$86.40	6.514%	$92.0281	$92.03	$92.05	$92.00
Purchase #7	$181.37	3.280%	$187.3189	$187.32	$187.30	$187.30
7 purchase totals =	$739.88		$805.3856	$805.40	$805.35	$805.30