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	$82.90	10.632%	$91.7139	$91.71	$91.70	$91.70
Purchase #2	$39.77	12.860%	$44.8844	$44.88	$44.90	$44.90
Purchase #3	$41.58	9.411%	$45.4931	$45.49	$45.50	$45.50
Purchase #4	$116.59	6.305%	$123.941	$123.94	$123.95	$123.90
Purchase #5	$32.28	10.295%	$35.6032	$35.60	$35.60	$35.60
Purchase #6	$176.93	11.602%	$197.4574	$197.46	$197.45	$197.50
Purchase #7	$236.28	8.743%	$256.938	$256.94	$256.95	$256.90
7 purchase totals =	$726.33		$796.0310	$796.02	$796.05	$796.00