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	$183.30	12.699%	$206.5773	$206.58	$206.60	$206.60
Purchase #2	$41.33	13.280%	$46.8186	$46.82	$46.80	$46.80
Purchase #3	$62.65	9.261%	$68.452	$68.45	$68.45	$68.50
Purchase #4	$123.51	6.529%	$131.574	$131.57	$131.55	$131.60
Purchase #5	$86.69	13.338%	$98.2527	$98.25	$98.25	$98.30
Purchase #6	$29.28	4.447%	$30.5821	$30.58	$30.60	$30.60
Purchase #7	$37.33	13.128%	$42.2307	$42.23	$42.25	$42.20
7 purchase totals =	$564.09		$624.4874	$624.48	$624.50	$624.60