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	$53.55	3.827%	$55.5994	$55.60	$55.60	$55.60
Purchase #2	$218.47	3.465%	$226.04	$226.04	$226.05	$226.00
Purchase #3	$131.90	5.404%	$139.0279	$139.03	$139.05	$139.00
Purchase #4	$165.43	5.649%	$174.7751	$174.78	$174.80	$174.80
Purchase #5	$66.84	5.162%	$70.2903	$70.29	$70.30	$70.30
Purchase #6	$90.48	4.540%	$94.5878	$94.59	$94.60	$94.60
Purchase #7	$248.68	12.340%	$279.3671	$279.37	$279.35	$279.40
7 purchase totals =	$975.35		$1,039.6876	$1,039.70	$1,039.75	$1,039.70