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	$250.80	3.422%	$259.3824	$259.38	$259.40	$259.40
Purchase #2	$37.25	9.621%	$40.8338	$40.83	$40.85	$40.80
Purchase #3	$160.45	6.624%	$171.0782	$171.08	$171.10	$171.10
Purchase #4	$90.52	8.470%	$98.187	$98.19	$98.20	$98.20
Purchase #5	$169.66	3.304%	$175.2656	$175.27	$175.25	$175.30
Purchase #6	$31.37	4.524%	$32.7892	$32.79	$32.80	$32.80
Purchase #7	$73.42	4.160%	$76.4743	$76.47	$76.45	$76.50
7 purchase totals =	$813.47		$854.0105	$854.01	$854.05	$854.10