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	$242.82	11.388%	$270.4723	$270.47	$270.45	$270.50
Purchase #2	$215.39	7.440%	$231.415	$231.42	$231.40	$231.40
Purchase #3	$176.60	8.393%	$191.422	$191.42	$191.40	$191.40
Purchase #4	$44.34	13.785%	$50.4523	$50.45	$50.45	$50.50
Purchase #5	$50.44	5.167%	$53.0462	$53.05	$53.05	$53.00
Purchase #6	$206.79	3.441%	$213.9056	$213.91	$213.90	$213.90
Purchase #7	$35.48	11.358%	$39.5098	$39.51	$39.50	$39.50
7 purchase totals =	$971.86		$1,050.2232	$1,050.23	$1,050.15	$1,050.20