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	$148.48	13.465%	$168.4728	$168.47	$168.45	$168.50
Purchase #2	$36.50	7.697%	$39.3094	$39.31	$39.30	$39.30
Purchase #3	$190.36	10.239%	$209.851	$209.85	$209.85	$209.90
Purchase #4	$134.64	13.699%	$153.0843	$153.08	$153.10	$153.10
Purchase #5	$224.25	10.341%	$247.4397	$247.44	$247.45	$247.40
Purchase #6	$70.40	11.464%	$78.4707	$78.47	$78.45	$78.50
Purchase #7	$145.60	13.103%	$164.678	$164.68	$164.70	$164.70
7 purchase totals =	$950.23		$1,061.3059	$1,061.30	$1,061.30	$1,061.40