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	$171.71	6.825%	$183.4292	$183.43	$183.45	$183.40
Purchase #2	$108.59	5.618%	$114.6906	$114.69	$114.70	$114.70
Purchase #3	$107.33	5.128%	$112.8339	$112.83	$112.85	$112.80
Purchase #4	$242.45	7.534%	$260.7162	$260.72	$260.70	$260.70
Purchase #5	$91.79	8.498%	$99.5903	$99.59	$99.60	$99.60
Purchase #6	$57.72	8.700%	$62.7416	$62.74	$62.75	$62.70
Purchase #7	$71.84	9.254%	$78.4881	$78.49	$78.50	$78.50
7 purchase totals =	$851.43		$912.4899	$912.49	$912.55	$912.40