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	$56.42	13.282%	$63.9137	$63.91	$63.90	$63.90
Purchase #2	$85.30	10.577%	$94.3222	$94.32	$94.30	$94.30
Purchase #3	$234.40	3.181%	$241.8563	$241.86	$241.85	$241.90
Purchase #4	$146.90	9.290%	$160.547	$160.55	$160.55	$160.50
Purchase #5	$144.58	13.482%	$164.0723	$164.07	$164.05	$164.10
Purchase #6	$236.30	8.613%	$256.6525	$256.65	$256.65	$256.70
Purchase #7	$61.60	9.579%	$67.5007	$67.50	$67.50	$67.50
7 purchase totals =	$965.50		$1,048.8647	$1,048.86	$1,048.80	$1,048.90