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	$105.58	13.203%	$119.5197	$119.52	$119.50	$119.50
Purchase #2	$150.88	3.122%	$155.5905	$155.59	$155.60	$155.60
Purchase #3	$248.93	6.783%	$265.8149	$265.81	$265.80	$265.80
Purchase #4	$91.40	7.519%	$98.2724	$98.27	$98.25	$98.30
Purchase #5	$36.38	10.775%	$40.2999	$40.30	$40.30	$40.30
Purchase #6	$41.79	10.589%	$46.2151	$46.22	$46.20	$46.20
Purchase #7	$244.49	13.417%	$277.2932	$277.29	$277.30	$277.30
7 purchase totals =	$919.45		$1,003.0057	$1,003.00	$1,002.95	$1,003.00