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	$78.29	3.650%	$81.1476	$81.15	$81.15	$81.10
Purchase #2	$207.77	11.863%	$232.4178	$232.42	$232.40	$232.40
Purchase #3	$201.58	4.848%	$211.3526	$211.35	$211.35	$211.40
Purchase #4	$72.95	13.637%	$82.8982	$82.90	$82.90	$82.90
Purchase #5	$15.50	13.324%	$17.5652	$17.57	$17.55	$17.60
Purchase #6	$33.29	6.337%	$35.3996	$35.40	$35.40	$35.40
Purchase #7	$99.25	12.380%	$111.5372	$111.54	$111.55	$111.50
7 purchase totals =	$708.63		$772.3182	$772.33	$772.30	$772.30