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	$146.48	8.246%	$158.5587	$158.56	$158.55	$158.60
Purchase #2	$40.74	3.707%	$42.2502	$42.25	$42.25	$42.30
Purchase #3	$16.61	12.139%	$18.6263	$18.63	$18.65	$18.60
Purchase #4	$64.59	11.668%	$72.1264	$72.13	$72.15	$72.10
Purchase #5	$229.31	4.585%	$239.8239	$239.82	$239.80	$239.80
Purchase #6	$14.61	3.711%	$15.1522	$15.15	$15.15	$15.20
Purchase #7	$98.39	8.763%	$107.0119	$107.01	$107.00	$107.00
7 purchase totals =	$610.73		$653.5496	$653.55	$653.55	$653.60