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	$204.46	7.491%	$219.7761	$219.78	$219.80	$219.80
Purchase #2	$164.85	12.610%	$185.6376	$185.64	$185.65	$185.60
Purchase #3	$115.98	6.785%	$123.8492	$123.85	$123.85	$123.80
Purchase #4	$189.73	7.583%	$204.1172	$204.12	$204.10	$204.10
Purchase #5	$126.58	13.199%	$143.2873	$143.29	$143.30	$143.30
Purchase #6	$93.83	5.559%	$99.046	$99.05	$99.05	$99.00
Purchase #7	$38.37	4.486%	$40.0913	$40.09	$40.10	$40.10
7 purchase totals =	$933.80		$1,015.8047	$1,015.82	$1,015.85	$1,015.70