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	$33.76	10.466%	$37.2933	$37.29	$37.30	$37.30
Purchase #2	$126.32	6.268%	$134.2377	$134.24	$134.25	$134.20
Purchase #3	$205.89	11.374%	$229.3079	$229.31	$229.30	$229.30
Purchase #4	$49.57	13.430%	$56.2273	$56.23	$56.25	$56.20
Purchase #5	$200.49	3.790%	$208.0886	$208.09	$208.10	$208.10
Purchase #6	$166.95	7.591%	$179.6232	$179.62	$179.60	$179.60
Purchase #7	$135.59	7.337%	$145.5382	$145.54	$145.55	$145.50
7 purchase totals =	$918.57		$990.3162	$990.32	$990.35	$990.20