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	$52.79	8.294%	$57.1684	$57.17	$57.15	$57.20
Purchase #2	$85.74	12.671%	$96.6041	$96.60	$96.60	$96.60
Purchase #3	$10.98	12.788%	$12.3841	$12.38	$12.40	$12.40
Purchase #4	$34.77	7.128%	$37.2484	$37.25	$37.25	$37.20
Purchase #5	$47.89	7.480%	$51.4722	$51.47	$51.45	$51.50
Purchase #6	$96.59	12.158%	$108.3334	$108.33	$108.35	$108.30
Purchase #7	$59.27	6.732%	$63.2601	$63.26	$63.25	$63.30
7 purchase totals =	$388.03		$426.4707	$426.46	$426.45	$426.50