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	$155.39	8.212%	$168.1506	$168.15	$168.15	$168.20
Purchase #2	$77.59	3.449%	$80.2661	$80.27	$80.25	$80.30
Purchase #3	$24.59	13.141%	$27.8214	$27.82	$27.80	$27.80
Purchase #4	$171.51	10.392%	$189.3333	$189.33	$189.35	$189.30
Purchase #5	$142.62	3.453%	$147.5447	$147.54	$147.55	$147.50
Purchase #6	$124.50	8.264%	$134.7887	$134.79	$134.80	$134.80
Purchase #7	$90.64	10.424%	$100.0883	$100.09	$100.10	$100.10
7 purchase totals =	$786.84		$847.9931	$847.99	$848.00	$848.00