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	$39.99	6.374%	$42.539	$42.54	$42.55	$42.50
Purchase #2	$81.49	4.475%	$85.1367	$85.14	$85.15	$85.10
Purchase #3	$242.48	13.447%	$275.0863	$275.09	$275.10	$275.10
Purchase #4	$203.90	13.661%	$231.7548	$231.75	$231.75	$231.80
Purchase #5	$34.64	9.131%	$37.803	$37.80	$37.80	$37.80
Purchase #6	$113.41	13.682%	$128.9268	$128.93	$128.95	$128.90
Purchase #7	$101.29	12.576%	$114.0282	$114.03	$114.05	$114.00
7 purchase totals =	$817.20		$915.2748	$915.28	$915.35	$915.20