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	$34.85	7.728%	$37.5432	$37.54	$37.55	$37.50
Purchase #2	$71.81	7.773%	$77.3918	$77.39	$77.40	$77.40
Purchase #3	$40.60	3.658%	$42.0851	$42.09	$42.10	$42.10
Purchase #4	$44.68	13.699%	$50.8007	$50.80	$50.80	$50.80
Purchase #5	$93.88	3.690%	$97.3442	$97.34	$97.35	$97.30
Purchase #6	$198.82	9.785%	$218.2745	$218.27	$218.25	$218.30
Purchase #7	$133.37	5.216%	$140.3266	$140.33	$140.35	$140.30
7 purchase totals =	$618.01		$663.7661	$663.76	$663.80	$663.70