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	$146.34	6.374%	$155.6677	$155.67	$155.65	$155.70
Purchase #2	$231.57	9.651%	$253.9188	$253.92	$253.90	$253.90
Purchase #3	$150.80	7.848%	$162.6348	$162.63	$162.65	$162.60
Purchase #4	$11.81	3.495%	$12.2228	$12.22	$12.20	$12.20
Purchase #5	$65.34	4.454%	$68.2502	$68.25	$68.25	$68.30
Purchase #6	$233.59	3.566%	$241.9198	$241.92	$241.90	$241.90
Purchase #7	$41.52	10.534%	$45.8937	$45.89	$45.90	$45.90
7 purchase totals =	$880.97		$940.5078	$940.50	$940.45	$940.50