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	$160.96	9.826%	$176.7759	$176.78	$176.80	$176.80
Purchase #2	$101.30	13.447%	$114.9218	$114.92	$114.90	$114.90
Purchase #3	$12.33	9.865%	$13.5464	$13.55	$13.55	$13.50
Purchase #4	$26.32	12.257%	$29.546	$29.55	$29.55	$29.50
Purchase #5	$155.37	6.551%	$165.5483	$165.55	$165.55	$165.50
Purchase #6	$63.85	3.601%	$66.1492	$66.15	$66.15	$66.10
Purchase #7	$147.83	4.397%	$154.3301	$154.33	$154.35	$154.30
7 purchase totals =	$667.96		$720.8177	$720.83	$720.85	$720.60