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	$127.31	8.814%	$138.5311	$138.53	$138.55	$138.50
Purchase #2	$140.87	7.642%	$151.6353	$151.64	$151.65	$151.60
Purchase #3	$236.88	10.460%	$261.6576	$261.66	$261.65	$261.70
Purchase #4	$46.52	13.169%	$52.6462	$52.65	$52.65	$52.60
Purchase #5	$51.48	5.239%	$54.177	$54.18	$54.20	$54.20
Purchase #6	$150.40	11.648%	$167.9186	$167.92	$167.90	$167.90
Purchase #7	$224.77	6.170%	$238.6383	$238.64	$238.65	$238.60
7 purchase totals =	$978.23		$1,065.2041	$1,065.22	$1,065.25	$1,065.10