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	$25.38	13.863%	$28.8984	$28.90	$28.90	$28.90
Purchase #2	$55.47	6.740%	$59.2087	$59.21	$59.20	$59.20
Purchase #3	$240.95	13.466%	$273.3963	$273.40	$273.40	$273.40
Purchase #4	$51.55	4.571%	$53.9064	$53.91	$53.90	$53.90
Purchase #5	$217.50	4.252%	$226.7481	$226.75	$226.75	$226.70
Purchase #6	$224.62	3.212%	$231.8348	$231.83	$231.85	$231.80
Purchase #7	$189.87	13.600%	$215.6923	$215.69	$215.70	$215.70
7 purchase totals =	$1,005.34		$1,089.6850	$1,089.69	$1,089.70	$1,089.60