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	$45.64	11.140%	$50.7243	$50.72	$50.70	$50.70
Purchase #2	$132.44	7.570%	$142.4657	$142.47	$142.45	$142.50
Purchase #3	$91.98	8.275%	$99.5913	$99.59	$99.60	$99.60
Purchase #4	$214.87	3.755%	$222.9384	$222.94	$222.95	$222.90
Purchase #5	$77.79	10.832%	$86.2162	$86.22	$86.20	$86.20
Purchase #6	$212.35	6.193%	$225.5008	$225.50	$225.50	$225.50
Purchase #7	$42.94	8.215%	$46.4675	$46.47	$46.45	$46.50
7 purchase totals =	$818.01		$873.9042	$873.91	$873.85	$873.90