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	$227.61	12.577%	$256.2365	$256.24	$256.25	$256.20
Purchase #2	$151.35	13.264%	$171.4251	$171.43	$171.45	$171.40
Purchase #3	$43.55	3.689%	$45.1566	$45.16	$45.15	$45.20
Purchase #4	$62.50	6.823%	$66.7644	$66.76	$66.75	$66.80
Purchase #5	$164.44	12.772%	$185.4423	$185.44	$185.45	$185.40
Purchase #6	$166.88	13.779%	$189.8744	$189.87	$189.85	$189.90
Purchase #7	$204.86	8.871%	$223.0331	$223.03	$223.05	$223.00
7 purchase totals =	$1,021.19		$1,137.9324	$1,137.93	$1,137.95	$1,137.90