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	$226.98	12.400%	$255.1255	$255.13	$255.15	$255.10
Purchase #2	$201.59	10.274%	$222.3014	$222.30	$222.30	$222.30
Purchase #3	$238.39	7.259%	$255.6947	$255.69	$255.70	$255.70
Purchase #4	$23.90	10.382%	$26.3813	$26.38	$26.40	$26.40
Purchase #5	$120.79	9.328%	$132.0573	$132.06	$132.05	$132.10
Purchase #6	$160.83	8.676%	$174.7836	$174.78	$174.80	$174.80
Purchase #7	$222.67	4.164%	$231.942	$231.94	$231.95	$231.90
7 purchase totals =	$1,195.15		$1,298.2858	$1,298.28	$1,298.35	$1,298.30