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	$88.72	12.688%	$99.9768	$99.98	$100.00	$100.00
Purchase #2	$27.31	13.834%	$31.0881	$31.09	$31.10	$31.10
Purchase #3	$212.92	5.384%	$224.3836	$224.38	$224.40	$224.40
Purchase #4	$212.97	7.799%	$229.5795	$229.58	$229.60	$229.60
Purchase #5	$80.63	12.692%	$90.8636	$90.86	$90.85	$90.90
Purchase #6	$236.71	9.329%	$258.7927	$258.79	$258.80	$258.80
Purchase #7	$20.54	10.307%	$22.6571	$22.66	$22.65	$22.70
7 purchase totals =	$879.80		$957.3414	$957.34	$957.40	$957.50