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	$11.32	9.514%	$12.397	$12.40	$12.40	$12.40
Purchase #2	$153.27	10.768%	$169.7741	$169.77	$169.75	$169.80
Purchase #3	$211.79	5.212%	$222.8285	$222.83	$222.85	$222.80
Purchase #4	$30.72	11.547%	$34.2672	$34.27	$34.25	$34.30
Purchase #5	$211.90	12.211%	$237.7751	$237.78	$237.80	$237.80
Purchase #6	$59.32	12.772%	$66.8964	$66.90	$66.90	$66.90
Purchase #7	$224.27	8.511%	$243.3576	$243.36	$243.35	$243.40
7 purchase totals =	$902.59		$987.2959	$987.31	$987.30	$987.40