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	$6.58	3.278%	$6.7957	$6.80	$6.80	$6.80
Purchase #2	$120.48	9.170%	$131.528	$131.53	$131.55	$131.50
Purchase #3	$246.40	4.401%	$257.2441	$257.24	$257.25	$257.20
Purchase #4	$91.59	8.135%	$99.0408	$99.04	$99.05	$99.00
Purchase #5	$36.30	3.348%	$37.5153	$37.52	$37.50	$37.50
Purchase #6	$117.53	8.384%	$127.3837	$127.38	$127.40	$127.40
Purchase #7	$97.52	9.578%	$106.8605	$106.86	$106.85	$106.90
7 purchase totals =	$716.40		$766.3681	$766.37	$766.40	$766.30