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	$43.97	4.822%	$46.0902	$46.09	$46.10	$46.10
Purchase #2	$126.31	4.552%	$132.0596	$132.06	$132.05	$132.10
Purchase #3	$168.97	8.570%	$183.4507	$183.45	$183.45	$183.50
Purchase #4	$82.86	8.830%	$90.1765	$90.18	$90.20	$90.20
Purchase #5	$222.49	12.402%	$250.0832	$250.08	$250.10	$250.10
Purchase #6	$36.94	9.285%	$40.3699	$40.37	$40.35	$40.40
Purchase #7	$51.34	11.456%	$57.2215	$57.22	$57.20	$57.20
7 purchase totals =	$732.88		$799.4516	$799.45	$799.45	$799.60