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	$239.71	8.789%	$260.7781	$260.78	$260.80	$260.80
Purchase #2	$130.44	13.736%	$148.3572	$148.36	$148.35	$148.40
Purchase #3	$153.69	3.705%	$159.3842	$159.38	$159.40	$159.40
Purchase #4	$149.68	4.825%	$156.9021	$156.90	$156.90	$156.90
Purchase #5	$90.31	5.540%	$95.3132	$95.31	$95.30	$95.30
Purchase #6	$215.65	10.572%	$238.4485	$238.45	$238.45	$238.40
Purchase #7	$105.95	12.177%	$118.8515	$118.85	$118.85	$118.90
7 purchase totals =	$1,085.43		$1,178.0348	$1,178.03	$1,178.05	$1,178.10