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	$134.58	3.619%	$139.4505	$139.45	$139.45	$139.50
Purchase #2	$85.82	4.107%	$89.3446	$89.34	$89.35	$89.30
Purchase #3	$241.80	6.281%	$256.9875	$256.99	$257.00	$257.00
Purchase #4	$82.34	3.240%	$85.0078	$85.01	$85.00	$85.00
Purchase #5	$157.45	8.694%	$171.1387	$171.14	$171.15	$171.10
Purchase #6	$187.43	6.403%	$199.4311	$199.43	$199.45	$199.40
Purchase #7	$87.41	8.447%	$94.7935	$94.79	$94.80	$94.80
7 purchase totals =	$976.83		$1,036.1537	$1,036.15	$1,036.20	$1,036.10