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	$150.91	13.730%	$171.6299	$171.63	$171.65	$171.60
Purchase #2	$230.75	13.242%	$261.3059	$261.31	$261.30	$261.30
Purchase #3	$82.29	9.184%	$89.8475	$89.85	$89.85	$89.80
Purchase #4	$219.51	8.694%	$238.5942	$238.59	$238.60	$238.60
Purchase #5	$65.59	13.751%	$74.6093	$74.61	$74.60	$74.60
Purchase #6	$108.27	10.687%	$119.8408	$119.84	$119.85	$119.80
Purchase #7	$41.30	5.472%	$43.5599	$43.56	$43.55	$43.60
7 purchase totals =	$898.62		$999.3875	$999.39	$999.40	$999.30