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	$62.44	10.375%	$68.9182	$68.92	$68.90	$68.90
Purchase #2	$36.96	3.847%	$38.3819	$38.38	$38.40	$38.40
Purchase #3	$95.53	3.522%	$98.8946	$98.89	$98.90	$98.90
Purchase #4	$198.36	9.486%	$217.1764	$217.18	$217.20	$217.20
Purchase #5	$218.25	9.440%	$238.8528	$238.85	$238.85	$238.90
Purchase #6	$57.52	13.778%	$65.4451	$65.45	$65.45	$65.40
Purchase #7	$78.66	5.274%	$82.8085	$82.81	$82.80	$82.80
7 purchase totals =	$747.72		$810.4775	$810.48	$810.50	$810.50