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	$95.27	8.702%	$103.5604	$103.56	$103.55	$103.60
Purchase #2	$71.65	4.815%	$75.0999	$75.10	$75.10	$75.10
Purchase #3	$185.32	12.692%	$208.8408	$208.84	$208.85	$208.80
Purchase #4	$60.60	9.301%	$66.2364	$66.24	$66.25	$66.20
Purchase #5	$100.49	11.229%	$111.774	$111.77	$111.75	$111.80
Purchase #6	$35.82	8.537%	$38.878	$38.88	$38.90	$38.90
Purchase #7	$138.41	12.722%	$156.0185	$156.02	$156.00	$156.00
7 purchase totals =	$687.56		$760.4080	$760.41	$760.40	$760.40