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	$227.96	12.561%	$256.5941	$256.59	$256.60	$256.60
Purchase #2	$145.91	6.680%	$155.6568	$155.66	$155.65	$155.70
Purchase #3	$174.62	12.715%	$196.8229	$196.82	$196.80	$196.80
Purchase #4	$59.74	12.175%	$67.0133	$67.01	$67.00	$67.00
Purchase #5	$163.68	13.671%	$186.0567	$186.06	$186.05	$186.10
Purchase #6	$92.54	6.414%	$98.4755	$98.48	$98.50	$98.50
Purchase #7	$169.35	13.451%	$192.1293	$192.13	$192.15	$192.10
7 purchase totals =	$1,033.80		$1,152.7486	$1,152.75	$1,152.75	$1,152.80