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	$39.61	5.724%	$41.8773	$41.88	$41.90	$41.90
Purchase #2	$87.84	5.786%	$92.9224	$92.92	$92.90	$92.90
Purchase #3	$142.45	9.173%	$155.5169	$155.52	$155.50	$155.50
Purchase #4	$198.57	6.168%	$210.8178	$210.82	$210.80	$210.80
Purchase #5	$83.97	9.322%	$91.7977	$91.80	$91.80	$91.80
Purchase #6	$24.34	12.207%	$27.3112	$27.31	$27.30	$27.30
Purchase #7	$100.65	3.267%	$103.9382	$103.94	$103.95	$103.90
7 purchase totals =	$677.43		$724.1815	$724.19	$724.15	$724.10