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	$117.74	10.716%	$130.357	$130.36	$130.35	$130.40
Purchase #2	$56.54	5.569%	$59.6887	$59.69	$59.70	$59.70
Purchase #3	$62.48	5.582%	$65.9676	$65.97	$65.95	$66.00
Purchase #4	$144.41	11.106%	$160.4482	$160.45	$160.45	$160.40
Purchase #5	$65.66	10.322%	$72.4374	$72.44	$72.45	$72.40
Purchase #6	$52.47	4.425%	$54.7918	$54.79	$54.80	$54.80
Purchase #7	$77.72	13.227%	$88	$88.00	$88.00	$88.00
7 purchase totals =	$577.02		$631.6907	$631.70	$631.70	$631.70