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	$206.66	3.240%	$213.3558	$213.36	$213.35	$213.40
Purchase #2	$59.86	10.687%	$66.2572	$66.26	$66.25	$66.30
Purchase #3	$28.59	10.434%	$31.5731	$31.57	$31.55	$31.60
Purchase #4	$224.67	11.490%	$250.4846	$250.48	$250.50	$250.50
Purchase #5	$102.60	8.723%	$111.5498	$111.55	$111.55	$111.50
Purchase #6	$79.44	4.194%	$82.7717	$82.77	$82.75	$82.80
Purchase #7	$45.61	5.874%	$48.2891	$48.29	$48.30	$48.30
7 purchase totals =	$747.43		$804.2813	$804.28	$804.25	$804.40