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	$80.52	11.580%	$89.8442	$89.84	$89.85	$89.80
Purchase #2	$63.93	5.599%	$67.5094	$67.51	$67.50	$67.50
Purchase #3	$50.26	11.115%	$55.8464	$55.85	$55.85	$55.80
Purchase #4	$92.55	3.758%	$96.028	$96.03	$96.05	$96.00
Purchase #5	$20.94	3.167%	$21.6032	$21.60	$21.60	$21.60
Purchase #6	$121.54	5.797%	$128.5857	$128.59	$128.60	$128.60
Purchase #7	$202.27	7.872%	$218.1927	$218.19	$218.20	$218.20
7 purchase totals =	$632.01		$677.6096	$677.61	$677.65	$677.50