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	$87.98	13.339%	$99.7157	$99.72	$99.70	$99.70
Purchase #2	$233.57	3.358%	$241.4133	$241.41	$241.40	$241.40
Purchase #3	$61.90	5.208%	$65.1238	$65.12	$65.10	$65.10
Purchase #4	$112.54	9.168%	$122.8577	$122.86	$122.85	$122.90
Purchase #5	$115.85	6.754%	$123.6745	$123.67	$123.65	$123.70
Purchase #6	$187.80	3.334%	$194.0613	$194.06	$194.05	$194.10
Purchase #7	$154.82	3.597%	$160.3889	$160.39	$160.40	$160.40
7 purchase totals =	$954.46		$1,007.2352	$1,007.23	$1,007.15	$1,007.30