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	$81.86	8.738%	$89.0129	$89.01	$89.00	$89.00
Purchase #2	$174.40	9.607%	$191.1546	$191.15	$191.15	$191.20
Purchase #3	$88.77	13.788%	$101.0096	$101.01	$101.00	$101.00
Purchase #4	$77.65	12.515%	$87.3679	$87.37	$87.35	$87.40
Purchase #5	$40.77	10.767%	$45.1597	$45.16	$45.15	$45.20
Purchase #6	$178.37	5.455%	$188.1001	$188.10	$188.10	$188.10
Purchase #7	$72.59	4.769%	$76.0518	$76.05	$76.05	$76.10
7 purchase totals =	$714.41		$777.8566	$777.85	$777.80	$778.00