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	$162.73	7.851%	$175.5059	$175.51	$175.50	$175.50
Purchase #2	$153.40	11.771%	$171.4567	$171.46	$171.45	$171.50
Purchase #3	$130.50	12.432%	$146.7238	$146.72	$146.70	$146.70
Purchase #4	$183.35	4.863%	$192.2663	$192.27	$192.25	$192.30
Purchase #5	$142.98	6.725%	$152.5954	$152.60	$152.60	$152.60
Purchase #6	$27.50	5.214%	$28.9339	$28.93	$28.95	$28.90
Purchase #7	$250.89	7.716%	$270.2487	$270.25	$270.25	$270.20
7 purchase totals =	$1,051.35		$1,137.7307	$1,137.74	$1,137.70	$1,137.70