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	$159.66	10.450%	$176.3445	$176.34	$176.35	$176.30
Purchase #2	$178.70	10.173%	$196.8792	$196.88	$196.90	$196.90
Purchase #3	$82.97	13.140%	$93.8723	$93.87	$93.85	$93.90
Purchase #4	$206.67	8.188%	$223.5921	$223.59	$223.60	$223.60
Purchase #5	$19.28	9.205%	$21.0547	$21.05	$21.05	$21.10
Purchase #6	$41.41	4.737%	$43.3716	$43.37	$43.35	$43.40
Purchase #7	$172.60	3.390%	$178.4511	$178.45	$178.45	$178.50
7 purchase totals =	$861.29		$933.5655	$933.55	$933.55	$933.70