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	$199.95	6.256%	$212.4589	$212.46	$212.45	$212.50
Purchase #2	$89.60	10.750%	$99.232	$99.23	$99.25	$99.20
Purchase #3	$16.89	7.118%	$18.0922	$18.09	$18.10	$18.10
Purchase #4	$43.73	10.425%	$48.2889	$48.29	$48.30	$48.30
Purchase #5	$242.50	5.383%	$255.5538	$255.55	$255.55	$255.60
Purchase #6	$67.37	5.493%	$71.0706	$71.07	$71.05	$71.10
Purchase #7	$179.26	4.725%	$187.73	$187.73	$187.75	$187.70
7 purchase totals =	$839.30		$892.4264	$892.42	$892.45	$892.50