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	$126.77	7.798%	$136.6555	$136.66	$136.65	$136.70
Purchase #2	$28.67	13.259%	$32.4714	$32.47	$32.45	$32.50
Purchase #3	$109.25	9.857%	$120.0188	$120.02	$120.00	$120.00
Purchase #4	$80.99	10.473%	$89.4721	$89.47	$89.45	$89.50
Purchase #5	$102.83	8.380%	$111.4472	$111.45	$111.45	$111.40
Purchase #6	$73.38	12.793%	$82.7675	$82.77	$82.75	$82.80
Purchase #7	$52.79	3.377%	$54.5727	$54.57	$54.55	$54.60
7 purchase totals =	$574.68		$627.4052	$627.41	$627.30	$627.50