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	$9.39	10.746%	$10.399	$10.40	$10.40	$10.40
Purchase #2	$21.65	3.741%	$22.4599	$22.46	$22.45	$22.50
Purchase #3	$77.80	7.439%	$83.5875	$83.59	$83.60	$83.60
Purchase #4	$8.85	11.520%	$9.8695	$9.87	$9.85	$9.90
Purchase #5	$53.70	10.410%	$59.2902	$59.29	$59.30	$59.30
Purchase #6	$149.83	5.390%	$157.9058	$157.91	$157.90	$157.90
Purchase #7	$33.80	12.210%	$37.927	$37.93	$37.95	$37.90
7 purchase totals =	$355.02		$381.4389	$381.45	$381.45	$381.50