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	$162.76	5.305%	$171.3944	$171.39	$171.40	$171.40
Purchase #2	$103.59	12.777%	$116.8257	$116.83	$116.85	$116.80
Purchase #3	$202.47	11.111%	$224.9664	$224.97	$224.95	$225.00
Purchase #4	$170.48	13.841%	$194.0761	$194.08	$194.10	$194.10
Purchase #5	$14.60	13.199%	$16.5271	$16.53	$16.55	$16.50
Purchase #6	$72.92	13.105%	$82.4762	$82.48	$82.50	$82.50
Purchase #7	$37.41	6.480%	$39.8342	$39.83	$39.85	$39.80
7 purchase totals =	$764.23		$846.1001	$846.11	$846.20	$846.10