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	$162.39	11.644%	$181.2987	$181.30	$181.30	$181.30
Purchase #2	$74.51	3.382%	$77.0299	$77.03	$77.05	$77.00
Purchase #3	$97.52	9.301%	$106.5903	$106.59	$106.60	$106.60
Purchase #4	$193.86	13.208%	$219.465	$219.47	$219.45	$219.50
Purchase #5	$94.93	8.113%	$102.6317	$102.63	$102.65	$102.60
Purchase #6	$248.26	13.549%	$281.8967	$281.90	$281.90	$281.90
Purchase #7	$126.50	3.656%	$131.1248	$131.12	$131.10	$131.10
7 purchase totals =	$997.97		$1,100.0371	$1,100.04	$1,100.05	$1,100.00