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	$164.79	10.304%	$181.77	$181.77	$181.75	$181.80
Purchase #2	$107.41	4.759%	$112.5216	$112.52	$112.50	$112.50
Purchase #3	$99.42	13.676%	$113.0167	$113.02	$113.00	$113.00
Purchase #4	$93.32	5.503%	$98.4554	$98.46	$98.45	$98.50
Purchase #5	$52.89	7.803%	$57.017	$57.02	$57.00	$57.00
Purchase #6	$137.70	13.736%	$156.6145	$156.61	$156.60	$156.60
Purchase #7	$79.80	4.692%	$83.5442	$83.54	$83.55	$83.50
7 purchase totals =	$735.33		$802.9394	$802.94	$802.85	$802.90