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	$177.96	3.335%	$183.895	$183.90	$183.90	$183.90
Purchase #2	$171.38	6.128%	$181.8822	$181.88	$181.90	$181.90
Purchase #3	$133.26	4.636%	$139.4379	$139.44	$139.45	$139.40
Purchase #4	$56.63	8.281%	$61.3195	$61.32	$61.30	$61.30
Purchase #5	$147.76	3.816%	$153.3985	$153.40	$153.40	$153.40
Purchase #6	$138.79	8.860%	$151.0868	$151.09	$151.10	$151.10
Purchase #7	$164.83	9.571%	$180.6059	$180.61	$180.60	$180.60
7 purchase totals =	$990.61		$1,051.6258	$1,051.64	$1,051.65	$1,051.60