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	$228.29	12.517%	$256.8651	$256.87	$256.85	$256.90
Purchase #2	$128.90	4.281%	$134.4182	$134.42	$134.40	$134.40
Purchase #3	$124.41	5.473%	$131.219	$131.22	$131.20	$131.20
Purchase #4	$161.37	6.295%	$171.5282	$171.53	$171.55	$171.50
Purchase #5	$225.70	4.769%	$236.4636	$236.46	$236.45	$236.50
Purchase #6	$135.77	3.167%	$140.0698	$140.07	$140.05	$140.10
Purchase #7	$57.31	5.599%	$60.5188	$60.52	$60.50	$60.50
7 purchase totals =	$1,061.75		$1,131.0827	$1,131.09	$1,131.00	$1,131.10