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	$90.83	8.827%	$98.8476	$98.85	$98.85	$98.80
Purchase #2	$90.91	10.755%	$100.6874	$100.69	$100.70	$100.70
Purchase #3	$54.80	9.497%	$60.0044	$60.00	$60.00	$60.00
Purchase #4	$87.78	3.402%	$90.7663	$90.77	$90.75	$90.80
Purchase #5	$149.29	4.805%	$156.4634	$156.46	$156.45	$156.50
Purchase #6	$186.34	6.872%	$199.1453	$199.15	$199.15	$199.10
Purchase #7	$76.38	9.255%	$83.449	$83.45	$83.45	$83.40
7 purchase totals =	$736.33		$789.3634	$789.37	$789.35	$789.30