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	$248.61	12.686%	$280.1487	$280.15	$280.15	$280.10
Purchase #2	$105.50	11.273%	$117.393	$117.39	$117.40	$117.40
Purchase #3	$135.71	11.733%	$151.6329	$151.63	$151.65	$151.60
Purchase #4	$14.55	6.144%	$15.444	$15.44	$15.45	$15.40
Purchase #5	$130.55	7.450%	$140.276	$140.28	$140.30	$140.30
Purchase #6	$209.35	10.575%	$231.4888	$231.49	$231.50	$231.50
Purchase #7	$77.40	11.162%	$86.0394	$86.04	$86.05	$86.00
7 purchase totals =	$921.67		$1,022.4228	$1,022.42	$1,022.50	$1,022.30