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	$90.91	11.171%	$101.0656	$101.07	$101.05	$101.10
Purchase #2	$98.93	4.659%	$103.5391	$103.54	$103.55	$103.50
Purchase #3	$126.50	9.649%	$138.706	$138.71	$138.70	$138.70
Purchase #4	$74.92	5.232%	$78.8398	$78.84	$78.85	$78.80
Purchase #5	$13.77	10.603%	$15.23	$15.23	$15.25	$15.20
Purchase #6	$139.26	9.687%	$152.7501	$152.75	$152.75	$152.80
Purchase #7	$47.72	5.312%	$50.2549	$50.25	$50.25	$50.30
7 purchase totals =	$592.01		$640.3855	$640.39	$640.40	$640.40