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	$227.46	9.654%	$249.419	$249.42	$249.40	$249.40
Purchase #2	$92.80	11.357%	$103.3393	$103.34	$103.35	$103.30
Purchase #3	$88.56	5.852%	$93.7425	$93.74	$93.75	$93.70
Purchase #4	$54.69	12.233%	$61.3802	$61.38	$61.40	$61.40
Purchase #5	$134.62	5.788%	$142.4118	$142.41	$142.40	$142.40
Purchase #6	$199.78	11.209%	$222.1733	$222.17	$222.15	$222.20
Purchase #7	$176.52	10.720%	$195.4429	$195.44	$195.45	$195.40
7 purchase totals =	$974.43		$1,067.9090	$1,067.90	$1,067.90	$1,067.80