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	$47.81	7.339%	$51.3188	$51.32	$51.30	$51.30
Purchase #2	$22.41	8.843%	$24.3917	$24.39	$24.40	$24.40
Purchase #3	$83.84	12.862%	$94.6235	$94.62	$94.60	$94.60
Purchase #4	$248.81	3.250%	$256.8963	$256.90	$256.90	$256.90
Purchase #5	$230.61	9.844%	$253.3112	$253.31	$253.30	$253.30
Purchase #6	$31.50	4.498%	$32.9169	$32.92	$32.90	$32.90
Purchase #7	$249.85	4.705%	$261.6054	$261.61	$261.60	$261.60
7 purchase totals =	$914.83		$975.0638	$975.07	$975.00	$975.00