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	$117.66	5.295%	$123.8901	$123.89	$123.90	$123.90
Purchase #2	$228.72	9.278%	$249.9406	$249.94	$249.95	$249.90
Purchase #3	$181.26	5.342%	$190.9429	$190.94	$190.95	$190.90
Purchase #4	$128.69	8.213%	$139.2593	$139.26	$139.25	$139.30
Purchase #5	$67.81	13.195%	$76.7575	$76.76	$76.75	$76.80
Purchase #6	$222.29	5.150%	$233.7379	$233.74	$233.75	$233.70
Purchase #7	$143.25	13.115%	$162.0372	$162.04	$162.05	$162.00
7 purchase totals =	$1,089.68		$1,176.5655	$1,176.57	$1,176.60	$1,176.50