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	$105.61	3.376%	$109.1754	$109.18	$109.20	$109.20
Purchase #2	$79.90	4.312%	$83.3453	$83.35	$83.35	$83.30
Purchase #3	$53.72	7.474%	$57.735	$57.74	$57.75	$57.70
Purchase #4	$108.32	4.708%	$113.4197	$113.42	$113.40	$113.40
Purchase #5	$173.92	4.366%	$181.5133	$181.51	$181.50	$181.50
Purchase #6	$130.80	6.681%	$139.5387	$139.54	$139.55	$139.50
Purchase #7	$103.77	8.181%	$112.2594	$112.26	$112.25	$112.30
7 purchase totals =	$756.04		$796.9868	$797.00	$797.00	$796.90