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	$47.40	12.211%	$53.188	$53.19	$53.20	$53.20
Purchase #2	$58.45	5.496%	$61.6624	$61.66	$61.65	$61.70
Purchase #3	$47.71	5.870%	$50.5106	$50.51	$50.50	$50.50
Purchase #4	$41.70	4.246%	$43.4706	$43.47	$43.45	$43.50
Purchase #5	$169.25	9.835%	$185.8957	$185.90	$185.90	$185.90
Purchase #6	$41.44	9.542%	$45.3942	$45.39	$45.40	$45.40
Purchase #7	$74.55	4.255%	$77.7221	$77.72	$77.70	$77.70
7 purchase totals =	$480.50		$517.8436	$517.84	$517.80	$517.90