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	$94.85	6.472%	$100.9887	$100.99	$101.00	$101.00
Purchase #2	$139.32	3.825%	$144.649	$144.65	$144.65	$144.60
Purchase #3	$87.26	3.742%	$90.5253	$90.53	$90.55	$90.50
Purchase #4	$47.81	10.286%	$52.7277	$52.73	$52.75	$52.70
Purchase #5	$133.51	13.787%	$151.917	$151.92	$151.90	$151.90
Purchase #6	$119.31	12.681%	$134.4397	$134.44	$134.45	$134.40
Purchase #7	$153.99	3.452%	$159.3057	$159.31	$159.30	$159.30
7 purchase totals =	$776.05		$834.5531	$834.57	$834.60	$834.40