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	$86.40	5.230%	$90.9187	$90.92	$90.90	$90.90
Purchase #2	$163.68	12.162%	$183.5868	$183.59	$183.60	$183.60
Purchase #3	$68.82	12.183%	$77.2043	$77.20	$77.20	$77.20
Purchase #4	$28.68	9.438%	$31.3868	$31.39	$31.40	$31.40
Purchase #5	$78.46	6.221%	$83.341	$83.34	$83.35	$83.30
Purchase #6	$114.51	13.485%	$129.9517	$129.95	$129.95	$130.00
Purchase #7	$248.28	4.506%	$259.4675	$259.47	$259.45	$259.50
7 purchase totals =	$788.83		$855.8568	$855.86	$855.85	$855.90