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	$128.71	12.420%	$144.6958	$144.70	$144.70	$144.70
Purchase #2	$49.84	4.123%	$51.8949	$51.89	$51.90	$51.90
Purchase #3	$135.28	12.595%	$152.3185	$152.32	$152.30	$152.30
Purchase #4	$6.77	8.337%	$7.3344	$7.33	$7.35	$7.30
Purchase #5	$95.64	3.321%	$98.8162	$98.82	$98.80	$98.80
Purchase #6	$174.27	5.253%	$183.4244	$183.42	$183.40	$183.40
Purchase #7	$235.86	12.348%	$264.984	$264.98	$265.00	$265.00
7 purchase totals =	$826.37		$903.4682	$903.46	$903.45	$903.40