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	$221.38	11.798%	$247.4984	$247.50	$247.50	$247.50
Purchase #2	$163.61	13.303%	$185.375	$185.38	$185.40	$185.40
Purchase #3	$114.59	5.758%	$121.1881	$121.19	$121.20	$121.20
Purchase #4	$72.66	12.496%	$81.7396	$81.74	$81.75	$81.70
Purchase #5	$28.95	7.319%	$31.0689	$31.07	$31.05	$31.10
Purchase #6	$72.89	13.724%	$82.8934	$82.89	$82.90	$82.90
Purchase #7	$33.33	10.459%	$36.816	$36.82	$36.80	$36.80
7 purchase totals =	$707.41		$786.5794	$786.59	$786.60	$786.60