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	$27.42	13.116%	$31.0164	$31.02	$31.00	$31.00
Purchase #2	$163.92	3.581%	$169.79	$169.79	$169.80	$169.80
Purchase #3	$50.92	13.643%	$57.867	$57.87	$57.85	$57.90
Purchase #4	$212.26	5.680%	$224.3164	$224.32	$224.30	$224.30
Purchase #5	$82.71	8.145%	$89.4467	$89.45	$89.45	$89.40
Purchase #6	$189.61	9.867%	$208.3188	$208.32	$208.30	$208.30
Purchase #7	$65.59	10.469%	$72.4566	$72.46	$72.45	$72.50
7 purchase totals =	$792.43		$853.2119	$853.23	$853.15	$853.20