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	$238.94	8.838%	$260.0575	$260.06	$260.05	$260.10
Purchase #2	$164.52	12.513%	$185.1064	$185.11	$185.10	$185.10
Purchase #3	$185.72	11.429%	$206.9459	$206.95	$206.95	$206.90
Purchase #4	$69.25	4.523%	$72.3822	$72.38	$72.40	$72.40
Purchase #5	$31.33	4.127%	$32.623	$32.62	$32.60	$32.60
Purchase #6	$223.71	7.607%	$240.7276	$240.73	$240.75	$240.70
Purchase #7	$230.51	11.668%	$257.4059	$257.41	$257.40	$257.40
7 purchase totals =	$1,143.98		$1,255.2485	$1,255.26	$1,255.25	$1,255.20