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	$248.72	8.381%	$269.5652	$269.57	$269.55	$269.60
Purchase #2	$75.55	13.146%	$85.4818	$85.48	$85.50	$85.50
Purchase #3	$159.45	7.504%	$171.4151	$171.42	$171.40	$171.40
Purchase #4	$107.80	10.229%	$118.8269	$118.83	$118.85	$118.80
Purchase #5	$230.29	12.486%	$259.044	$259.04	$259.05	$259.00
Purchase #6	$123.88	10.848%	$137.3185	$137.32	$137.30	$137.30
Purchase #7	$169.74	9.674%	$186.1606	$186.16	$186.15	$186.20
7 purchase totals =	$1,115.43		$1,227.8121	$1,227.82	$1,227.80	$1,227.80