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	$238.89	4.661%	$250.0247	$250.02	$250.00	$250.00
Purchase #2	$90.87	5.531%	$95.896	$95.90	$95.90	$95.90
Purchase #3	$129.75	4.799%	$135.9767	$135.98	$136.00	$136.00
Purchase #4	$146.85	7.869%	$158.4056	$158.41	$158.40	$158.40
Purchase #5	$112.52	7.337%	$120.7756	$120.78	$120.80	$120.80
Purchase #6	$138.67	4.813%	$145.3442	$145.34	$145.35	$145.30
Purchase #7	$128.77	3.184%	$132.87	$132.87	$132.85	$132.90
7 purchase totals =	$986.32		$1,039.2928	$1,039.30	$1,039.30	$1,039.30