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	$26.27	7.450%	$28.2271	$28.23	$28.25	$28.20
Purchase #2	$141.55	3.410%	$146.3769	$146.38	$146.40	$146.40
Purchase #3	$201.66	11.695%	$225.2441	$225.24	$225.25	$225.20
Purchase #4	$116.60	4.644%	$122.0149	$122.01	$122.00	$122.00
Purchase #5	$177.61	12.374%	$199.5875	$199.59	$199.60	$199.60
Purchase #6	$153.75	7.183%	$164.7939	$164.79	$164.80	$164.80
Purchase #7	$90.57	10.754%	$100.3099	$100.31	$100.30	$100.30
7 purchase totals =	$908.01		$986.5543	$986.55	$986.60	$986.50