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	$6.90	13.661%	$7.8426	$7.84	$7.85	$7.80
Purchase #2	$35.56	12.357%	$39.9541	$39.95	$39.95	$40.00
Purchase #3	$40.98	9.676%	$44.9452	$44.95	$44.95	$44.90
Purchase #4	$81.51	4.551%	$85.2195	$85.22	$85.20	$85.20
Purchase #5	$100.72	3.676%	$104.4225	$104.42	$104.40	$104.40
Purchase #6	$75.45	10.738%	$83.5518	$83.55	$83.55	$83.60
Purchase #7	$245.79	3.832%	$255.2087	$255.21	$255.20	$255.20
7 purchase totals =	$586.91		$621.1444	$621.14	$621.10	$621.10