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	$110.57	11.842%	$123.6637	$123.66	$123.65	$123.70
Purchase #2	$106.38	11.362%	$118.4669	$118.47	$118.45	$118.50
Purchase #3	$59.83	9.540%	$65.5378	$65.54	$65.55	$65.50
Purchase #4	$99.72	12.355%	$112.0404	$112.04	$112.05	$112.00
Purchase #5	$29.80	5.553%	$31.4548	$31.45	$31.45	$31.50
Purchase #6	$45.89	8.358%	$49.7255	$49.73	$49.75	$49.70
Purchase #7	$247.86	5.137%	$260.5926	$260.59	$260.60	$260.60
7 purchase totals =	$700.05		$761.4817	$761.48	$761.50	$761.50