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	$40.62	6.688%	$43.3367	$43.34	$43.35	$43.30
Purchase #2	$246.61	8.445%	$267.4362	$267.44	$267.45	$267.40
Purchase #3	$43.27	5.640%	$45.7104	$45.71	$45.70	$45.70
Purchase #4	$72.49	11.131%	$80.5589	$80.56	$80.55	$80.60
Purchase #5	$99.26	13.384%	$112.545	$112.55	$112.55	$112.50
Purchase #6	$147.52	4.237%	$153.7704	$153.77	$153.75	$153.80
Purchase #7	$231.92	10.170%	$255.5063	$255.51	$255.50	$255.50
7 purchase totals =	$881.69		$958.8639	$958.88	$958.85	$958.80