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	$166.96	3.256%	$172.3962	$172.40	$172.40	$172.40
Purchase #2	$32.86	11.820%	$36.7441	$36.74	$36.75	$36.70
Purchase #3	$130.79	4.814%	$137.0862	$137.09	$137.10	$137.10
Purchase #4	$243.38	5.575%	$256.9484	$256.95	$256.95	$256.90
Purchase #5	$148.30	5.748%	$156.8243	$156.82	$156.80	$156.80
Purchase #6	$224.36	11.614%	$250.4172	$250.42	$250.40	$250.40
Purchase #7	$228.90	13.856%	$260.6164	$260.62	$260.60	$260.60
7 purchase totals =	$1,175.55		$1,271.0328	$1,271.04	$1,271.00	$1,270.90