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	$72.50	13.720%	$82.447	$82.45	$82.45	$82.40
Purchase #2	$41.78	9.320%	$45.6739	$45.67	$45.65	$45.70
Purchase #3	$96.45	9.631%	$105.7391	$105.74	$105.75	$105.70
Purchase #4	$90.26	9.839%	$99.1407	$99.14	$99.15	$99.10
Purchase #5	$101.73	4.130%	$105.9314	$105.93	$105.95	$105.90
Purchase #6	$78.64	7.761%	$84.7433	$84.74	$84.75	$84.70
Purchase #7	$121.53	8.578%	$131.9548	$131.95	$131.95	$132.00
7 purchase totals =	$602.89		$655.6302	$655.62	$655.65	$655.50