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	$142.51	11.787%	$159.3077	$159.31	$159.30	$159.30
Purchase #2	$90.73	13.823%	$103.2716	$103.27	$103.25	$103.30
Purchase #3	$154.49	8.674%	$167.8905	$167.89	$167.90	$167.90
Purchase #4	$42.41	13.750%	$48.2414	$48.24	$48.25	$48.20
Purchase #5	$134.98	4.192%	$140.6384	$140.64	$140.65	$140.60
Purchase #6	$243.33	10.574%	$269.0597	$269.06	$269.05	$269.10
Purchase #7	$11.54	7.447%	$12.3994	$12.40	$12.40	$12.40
7 purchase totals =	$819.99		$900.8087	$900.81	$900.80	$900.80