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	$20.96	3.790%	$21.7544	$21.75	$21.75	$21.80
Purchase #2	$114.52	11.601%	$127.8055	$127.81	$127.80	$127.80
Purchase #3	$131.43	5.624%	$138.8216	$138.82	$138.80	$138.80
Purchase #4	$178.55	5.224%	$187.8775	$187.88	$187.90	$187.90
Purchase #5	$90.27	11.351%	$100.5165	$100.52	$100.50	$100.50
Purchase #6	$202.98	12.363%	$228.0744	$228.07	$228.05	$228.10
Purchase #7	$231.98	3.828%	$240.8602	$240.86	$240.85	$240.90
7 purchase totals =	$970.69		$1,045.7101	$1,045.71	$1,045.65	$1,045.80