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	$150.89	13.346%	$171.0278	$171.03	$171.05	$171.00
Purchase #2	$213.50	12.522%	$240.2345	$240.23	$240.25	$240.20
Purchase #3	$151.39	5.828%	$160.213	$160.21	$160.20	$160.20
Purchase #4	$50.38	12.355%	$56.6044	$56.60	$56.60	$56.60
Purchase #5	$39.59	3.762%	$41.0794	$41.08	$41.10	$41.10
Purchase #6	$194.77	12.384%	$218.8903	$218.89	$218.90	$218.90
Purchase #7	$103.93	9.763%	$114.0767	$114.08	$114.10	$114.10
7 purchase totals =	$904.45		$1,002.1261	$1,002.12	$1,002.20	$1,002.10