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	$144.72	9.600%	$158.6131	$158.61	$158.60	$158.60
Purchase #2	$98.47	5.400%	$103.7874	$103.79	$103.80	$103.80
Purchase #3	$130.64	12.599%	$147.0993	$147.10	$147.10	$147.10
Purchase #4	$113.57	8.715%	$123.4676	$123.47	$123.45	$123.50
Purchase #5	$21.87	12.806%	$24.6707	$24.67	$24.65	$24.70
Purchase #6	$167.75	10.385%	$185.1708	$185.17	$185.15	$185.20
Purchase #7	$212.39	12.169%	$238.2357	$238.24	$238.25	$238.20
7 purchase totals =	$889.41		$981.0446	$981.05	$981.00	$981.10