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	$19.59	4.551%	$20.4815	$20.48	$20.50	$20.50
Purchase #2	$33.74	8.442%	$36.5883	$36.59	$36.60	$36.60
Purchase #3	$245.96	5.140%	$258.6023	$258.60	$258.60	$258.60
Purchase #4	$148.25	13.594%	$168.4031	$168.40	$168.40	$168.40
Purchase #5	$102.33	11.704%	$114.3067	$114.31	$114.30	$114.30
Purchase #6	$140.87	4.683%	$147.4669	$147.47	$147.45	$147.50
Purchase #7	$87.78	5.836%	$92.9028	$92.90	$92.90	$92.90
7 purchase totals =	$778.52		$838.7516	$838.75	$838.75	$838.80