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	$135.79	10.313%	$149.794	$149.79	$149.80	$149.80
Purchase #2	$81.83	9.146%	$89.3142	$89.31	$89.30	$89.30
Purchase #3	$144.59	8.443%	$156.7977	$156.80	$156.80	$156.80
Purchase #4	$20.79	6.291%	$22.0979	$22.10	$22.10	$22.10
Purchase #5	$135.90	7.372%	$145.9185	$145.92	$145.90	$145.90
Purchase #6	$228.41	4.231%	$238.074	$238.07	$238.05	$238.10
Purchase #7	$117.31	12.482%	$131.9526	$131.95	$131.95	$132.00
7 purchase totals =	$864.62		$933.9489	$933.94	$933.90	$934.00