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	$116.94	5.507%	$123.3799	$123.38	$123.40	$123.40
Purchase #2	$236.43	13.789%	$269.0313	$269.03	$269.05	$269.00
Purchase #3	$56.98	10.514%	$62.9709	$62.97	$62.95	$63.00
Purchase #4	$100.31	13.660%	$114.0123	$114.01	$114.00	$114.00
Purchase #5	$35.90	11.109%	$39.8881	$39.89	$39.90	$39.90
Purchase #6	$54.53	8.302%	$59.0571	$59.06	$59.05	$59.10
Purchase #7	$58.60	6.457%	$62.3838	$62.38	$62.40	$62.40
7 purchase totals =	$659.69		$730.7234	$730.72	$730.75	$730.80