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	$56.27	6.329%	$59.8313	$59.83	$59.85	$59.80
Purchase #2	$144.83	9.367%	$158.3962	$158.40	$158.40	$158.40
Purchase #3	$170.83	9.423%	$186.9273	$186.93	$186.95	$186.90
Purchase #4	$135.32	12.243%	$151.8872	$151.89	$151.90	$151.90
Purchase #5	$164.34	10.318%	$181.2966	$181.30	$181.30	$181.30
Purchase #6	$41.77	5.106%	$43.9028	$43.90	$43.90	$43.90
Purchase #7	$14.87	6.370%	$15.8172	$15.82	$15.80	$15.80
7 purchase totals =	$728.23		$798.0586	$798.07	$798.10	$798.00