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	$6.80	3.554%	$7.0417	$7.04	$7.05	$7.00
Purchase #2	$194.46	9.256%	$212.4592	$212.46	$212.45	$212.50
Purchase #3	$215.38	4.212%	$224.4518	$224.45	$224.45	$224.50
Purchase #4	$167.46	8.396%	$181.5199	$181.52	$181.50	$181.50
Purchase #5	$194.55	9.390%	$212.8182	$212.82	$212.80	$212.80
Purchase #6	$66.56	8.283%	$72.0732	$72.07	$72.05	$72.10
Purchase #7	$162.61	4.109%	$169.2916	$169.29	$169.30	$169.30
7 purchase totals =	$1,007.82		$1,079.6556	$1,079.65	$1,079.60	$1,079.70