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	$138.39	4.357%	$144.4197	$144.42	$144.40	$144.40
Purchase #2	$200.89	7.480%	$215.9166	$215.92	$215.90	$215.90
Purchase #3	$79.76	4.344%	$83.2248	$83.22	$83.20	$83.20
Purchase #4	$143.85	3.121%	$148.3396	$148.34	$148.35	$148.30
Purchase #5	$34.86	8.631%	$37.8688	$37.87	$37.85	$37.90
Purchase #6	$35.25	4.795%	$36.9402	$36.94	$36.95	$36.90
Purchase #7	$116.72	3.786%	$121.139	$121.14	$121.15	$121.10
7 purchase totals =	$749.72		$787.8487	$787.85	$787.80	$787.70