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	$111.38	5.167%	$117.135	$117.14	$117.15	$117.10
Purchase #2	$74.42	10.701%	$82.3837	$82.38	$82.40	$82.40
Purchase #3	$47.62	6.832%	$50.8734	$50.87	$50.85	$50.90
Purchase #4	$164.46	10.254%	$181.3237	$181.32	$181.30	$181.30
Purchase #5	$100.42	7.574%	$108.0258	$108.03	$108.05	$108.00
Purchase #6	$73.81	11.727%	$82.4657	$82.47	$82.45	$82.50
Purchase #7	$141.78	13.147%	$160.4198	$160.42	$160.40	$160.40
7 purchase totals =	$713.89		$782.6271	$782.63	$782.60	$782.60