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	$124.46	9.282%	$136.0124	$136.01	$136.00	$136.00
Purchase #2	$114.33	9.224%	$124.8758	$124.88	$124.90	$124.90
Purchase #3	$139.40	8.384%	$151.0873	$151.09	$151.10	$151.10
Purchase #4	$50.59	10.538%	$55.9212	$55.92	$55.90	$55.90
Purchase #5	$36.83	5.515%	$38.8612	$38.86	$38.85	$38.90
Purchase #6	$125.53	5.480%	$132.409	$132.41	$132.40	$132.40
Purchase #7	$78.95	4.387%	$82.4135	$82.41	$82.40	$82.40
7 purchase totals =	$670.09		$721.5804	$721.58	$721.55	$721.60