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	$239.98	4.418%	$250.5823	$250.58	$250.60	$250.60
Purchase #2	$181.53	5.850%	$192.1495	$192.15	$192.15	$192.10
Purchase #3	$142.99	3.141%	$147.4813	$147.48	$147.50	$147.50
Purchase #4	$142.54	10.751%	$157.8645	$157.86	$157.85	$157.90
Purchase #5	$132.91	5.671%	$140.4473	$140.45	$140.45	$140.40
Purchase #6	$82.69	8.413%	$89.6467	$89.65	$89.65	$89.60
Purchase #7	$222.28	6.750%	$237.2839	$237.28	$237.30	$237.30
7 purchase totals =	$1,144.92		$1,215.4555	$1,215.45	$1,215.50	$1,215.40