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	$212.83	5.195%	$223.8865	$223.89	$223.90	$223.90
Purchase #2	$106.87	5.170%	$112.3952	$112.40	$112.40	$112.40
Purchase #3	$47.44	13.844%	$54.0076	$54.01	$54.00	$54.00
Purchase #4	$47.49	4.164%	$49.4675	$49.47	$49.45	$49.50
Purchase #5	$223.31	8.710%	$242.7603	$242.76	$242.75	$242.80
Purchase #6	$11.60	7.141%	$12.4284	$12.43	$12.45	$12.40
Purchase #7	$178.78	4.369%	$186.5909	$186.59	$186.60	$186.60
7 purchase totals =	$828.32		$881.5364	$881.55	$881.55	$881.60