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	$58.44	12.374%	$65.6714	$65.67	$65.65	$65.70
Purchase #2	$74.91	9.800%	$82.2512	$82.25	$82.25	$82.30
Purchase #3	$152.74	13.182%	$172.8742	$172.87	$172.85	$172.90
Purchase #4	$190.47	5.775%	$201.4696	$201.47	$201.45	$201.50
Purchase #5	$25.81	4.632%	$27.0055	$27.01	$27.00	$27.00
Purchase #6	$59.86	8.559%	$64.9834	$64.98	$65.00	$65.00
Purchase #7	$61.60	9.433%	$67.4107	$67.41	$67.40	$67.40
7 purchase totals =	$623.83		$681.6660	$681.66	$681.60	$681.80