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	$123.96	9.763%	$136.0622	$136.06	$136.05	$136.10
Purchase #2	$14.26	11.761%	$15.9371	$15.94	$15.95	$15.90
Purchase #3	$40.38	3.258%	$41.6956	$41.70	$41.70	$41.70
Purchase #4	$162.78	13.691%	$185.0662	$185.07	$185.05	$185.10
Purchase #5	$27.75	5.467%	$29.2671	$29.27	$29.25	$29.30
Purchase #6	$173.79	13.243%	$196.805	$196.81	$196.80	$196.80
Purchase #7	$199.59	10.380%	$220.3074	$220.31	$220.30	$220.30
7 purchase totals =	$742.51		$825.1406	$825.16	$825.10	$825.20